feat(cli): add skill subcommand for knowledge skill management

New `stackmemory skill` command for managing .skill.md knowledge files:
- list: discover skills from global + project dirs
- match: keyword-match skills against a prompt
- show: display full skill content
- add: install from local file or URL
- refresh: check freshness, flag expired skills
- init: scaffold new .skill.md with template

Author: StackMemory Bot (CLI)

.claude/skills/knowledge/better-sqlite3.skill.md

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+---
+name: better-sqlite3
+version: 2025.12.1
+domain: database
+expires: 2026-12-01
+activates_on: [sqlite, better-sqlite3, database, db, query, fts, fts5, pragma, wal, transaction]
+sources:
+  - https://github.com/WiseLibs/better-sqlite3/blob/master/docs/api.md
+context7: WiseLibs/better-sqlite3
+---
+
+# better-sqlite3
+
+## Basics
+- Open: `new Database(path)` or `new Database(':memory:')`
+- **Synchronous API** — no async/await, no callbacks
+- Prepare + run: `db.prepare('SELECT * FROM t WHERE id = ?').get(id)`
+- All rows: `.all(params)` | Single row: `.get(params)` | Execute: `.run(params)`
+- Params: positional `?` or named `$name` / `:name` / `@name`
+
+## Transactions
+```js
+const insert = db.prepare('INSERT INTO t (a, b) VALUES (?, ?)');
+const insertMany = db.transaction((items) => {
+  for (const item of items) insert.run(item.a, item.b);
+});
+insertMany(items); // atomic, auto-rollback on error
+```
+- `db.transaction()` returns a reusable function — best pattern for batch ops
+- Nested transactions: use `.deferred()`, `.immediate()`, `.exclusive()`
+
+## FTS5 (Full-Text Search)
+- Create: `CREATE VIRTUAL TABLE t_fts USING fts5(content, tokenize='porter unicode61')`
+- Search: `SELECT * FROM t_fts WHERE t_fts MATCH 'query'`
+- Rank: `SELECT *, rank FROM t_fts WHERE t_fts MATCH 'query' ORDER BY rank`
+- BM25: `SELECT *, bm25(t_fts) as score FROM t_fts WHERE t_fts MATCH ?`
+- Highlight: `highlight(t_fts, 0, '<b>', '</b>')`
+
+## WAL Mode
+- Enable: `db.pragma('journal_mode = WAL')` — concurrent reads, single writer
+- Always enable for production — significant performance improvement
+- `db.pragma('busy_timeout = 5000')` — wait up to 5s for write lock
+
+## Performance
+- `db.pragma('cache_size = -64000')` — 64MB cache
+- `db.pragma('synchronous = NORMAL')` — faster writes (WAL mode safe)
+- `db.prepare()` caches the statement plan — reuse prepared statements
+- Batch inserts: always wrap in `db.transaction()` — 100x faster than individual inserts
+
+## ESM Import
+- CJS native addon: `import Database from 'better-sqlite3'`
+- Mark as `external` in esbuild — can't bundle native `.node` files
+- Prebuilt binaries: `npm install` downloads correct platform binary
+
+## Gotchas
+- Synchronous — blocks event loop on large queries; use worker_threads for heavy ops
+- `.get()` returns `undefined` if no row (not `null`)
+- `.run()` returns `{ changes, lastInsertRowid }` — not the row itself
+- Column names are case-sensitive in result objects
+- VACUUM: locks entire DB — run during maintenance windows only

.claude/skills/knowledge/commander-cli.skill.md

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+---
+name: commander-cli
+version: 2025.12.1
+domain: cli
+expires: 2026-12-01
+activates_on: [commander, cli, command, option, argument, subcommand, parse, program, action]
+sources:
+  - https://github.com/tj/commander.js#readme
+context7: tj/commander.js
+---
+
+# Commander.js CLI Framework
+
+## Basic Setup
+```ts
+import { Command } from 'commander';
+const program = new Command();
+program
+  .name('mycli')
+  .version('1.0.0')
+  .description('description');
+```
+
+## Commands
+```ts
+program
+  .command('serve')
+  .description('Start server')
+  .option('-p, --port <number>', 'port', '3000')
+  .option('-v, --verbose', 'verbose output')
+  .argument('<dir>', 'directory to serve')
+  .action((dir, options) => {
+    console.log(dir, options.port, options.verbose);
+  });
+```
+
+## Subcommands
+```ts
+const parent = program.command('db');
+parent.command('migrate').action(() => { ... });
+parent.command('seed').action(() => { ... });
+// Usage: mycli db migrate
+```
+
+## Options
+- Required value: `-p, --port <number>` (angle brackets)
+- Optional value: `-p, --port [number]` (square brackets)
+- Boolean flag: `-v, --verbose` (no value)
+- Variadic: `-f, --files <items...>` (collects into array)
+- Default: `.option('-p, --port <n>', 'desc', '3000')`
+- Choices: `.addOption(new Option('--env <e>').choices(['dev', 'prod']))`
+- Negatable: `--no-color` (sets `options.color = false`)
+
+## Patterns for This Project
+- 70+ commands — use subcommand groups (`skill`, `frame`, `session`, `linear`, etc.)
+- Action handlers: async functions with try/catch + `process.exit(1)` on error
+- Global options: define on `program` before subcommands
+- Help: auto-generated — add `.addHelpText('after', text)` for examples
+
+## Gotchas
+- Option values are strings by default — parse with `.argParser(parseInt)` or coerce in action
+- `program.parse()` must be called last (or `program.parseAsync()` for async actions)
+- `.command('*')` for catch-all unknown commands
+- Negative options: `--no-foo` creates `options.foo = false` — conflicts if `--foo` also defined
+- ESM: Commander works fine, but ensure `#!/usr/bin/env node` in bin entry

.claude/skills/knowledge/esbuild-esm.skill.md

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+---
+name: esbuild-esm
+version: 2025.12.1
+domain: build
+expires: 2026-12-01
+activates_on: [esbuild, build, bundle, esm, import, export, module, cjs, commonjs, dist, entry]
+sources:
+  - https://esbuild.github.io/api/
+  - https://nodejs.org/api/esm.html
+context7: evanw/esbuild
+---
+
+# esbuild + ESM
+
+## esbuild Config
+- Entry: `esbuild.build({ entryPoints, bundle, platform, format, outdir })`
+- Platform: `'node'` for CLI tools (excludes node builtins from bundle)
+- Format: `'esm'` — this project is ESM-first (`"type": "module"` in package.json)
+- External: mark `better-sqlite3`, native addons as external (can't bundle .node files)
+- Sourcemaps: `sourcemap: true` for debugging
+
+## ESM Rules (Node.js)
+- **Always** add `.js` extension to relative imports: `import { foo } from './bar.js'`
+- `__dirname` / `__filename` not available — use `import.meta.url` + `fileURLToPath()`
+- `require()` not available — use `createRequire(import.meta.url)` for CJS interop
+- Top-level `await` works in ESM
+- JSON imports: `import data from './file.json' with { type: 'json' }` (or createRequire)
+
+## CJS Interop
+- Import CJS from ESM: default import works (`import pkg from 'cjs-pkg'`)
+- Named exports: may need `import pkg from 'pkg'; const { named } = pkg;`
+- `better-sqlite3`: CJS native addon — import as default, mark external in esbuild
+
+## Package.json
+- `"type": "module"` — all .js files are ESM
+- `"exports"` field for package entry points (not just "main")
+- `"bin"` field for CLI executables — ensure shebang `#!/usr/bin/env node`
+
+## Gotchas
+- Missing `.js` extension → `ERR_MODULE_NOT_FOUND` (most common error)
+- esbuild `bundle: true` inlines deps — use `external` for native modules
+- `--packages=external` excludes all node_modules (useful for dev builds)
+- Watch mode: `esbuild.context().then(ctx => ctx.watch())` — not `--watch` flag in API

.claude/skills/knowledge/mcp-protocol.skill.md

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+---
+name: mcp-protocol
+version: 2025.12.1
+domain: protocol
+expires: 2026-06-01
+activates_on: [mcp, model context protocol, tool, resource, prompt, server, transport, stdio, sse, streamable]
+sources:
+  - https://modelcontextprotocol.io/docs
+  - https://github.com/modelcontextprotocol/typescript-sdk
+context7: modelcontextprotocol/typescript-sdk
+---
+
+# Model Context Protocol (MCP)
+
+## SDK (@modelcontextprotocol/sdk)
+```ts
+import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
+import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
+
+const server = new McpServer({ name: 'my-server', version: '1.0.0' });
+```
+
+## Tools
+```ts
+server.tool('tool_name', 'description', {
+  param: z.string().describe('param description'),  // Zod schema
+}, async ({ param }) => {
+  return { content: [{ type: 'text', text: result }] };
+});
+```
+- Input schema: Zod objects auto-converted to JSON Schema
+- Return: `{ content: [{ type: 'text' | 'image' | 'resource', ... }] }`
+- Error: `{ isError: true, content: [{ type: 'text', text: errorMsg }] }`
+
+## Resources
+```ts
+server.resource('resource://uri', 'description', async (uri) => {
+  return { contents: [{ uri, mimeType: 'text/plain', text: data }] };
+});
+```
+- Static URI or template: `resource://users/{id}`
+- `list_changed` notification when resources update
+
+## Transports
+- **Stdio**: `StdioServerTransport` — for CLI-launched servers (Claude Code default)
+- **Streamable HTTP**: `StreamableHTTPServerTransport` — for networked servers
+- **SSE** (deprecated): use Streamable HTTP instead for new servers
+
+## Prompts
+```ts
+server.prompt('prompt_name', 'description', { arg: z.string() }, ({ arg }) => {
+  return { messages: [{ role: 'user', content: { type: 'text', text: `...${arg}...` } }] };
+});
+```
+
+## Client Side
+```ts
+import { Client } from '@modelcontextprotocol/sdk/client/index.js';
+const client = new Client({ name: 'my-client', version: '1.0.0' });
+await client.connect(transport);
+const result = await client.callTool({ name: 'tool_name', arguments: { param: 'value' } });
+```
+
+## Gotchas
+- Tool names: snake_case convention (not camelCase)
+- Stdio transport: server MUST NOT write to stdout except MCP messages (use stderr for logs)
+- Zod schemas: `.describe()` on each field — LLMs use descriptions for tool calling
+- Error handling: return error content, don't throw (throws crash the server)
+- Transport cleanup: `await server.close()` on shutdown

.claude/skills/knowledge/vitest.skill.md

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+---
+name: vitest
+version: 2025.12.1
+domain: testing
+expires: 2026-12-01
+activates_on: [vitest, test, spec, mock, spy, describe, it, expect, vi, beforeEach, coverage]
+sources:
+  - https://vitest.dev/api/
+  - https://vitest.dev/guide/mocking
+context7: vitest-dev/vitest
+---
+
+# Vitest
+
+## Config (this project)
+- Projects: unit, integration, live (API), bench
+- Coverage: v8 provider, thresholds: 25% statements, 20% branches, 30% functions
+- ESM native — no transform needed (unlike Jest + SWC)
+
+## API (differs from Jest)
+- Mock function: `vi.fn()` (not `jest.fn()`)
+- Mock module: `vi.mock('./module')` — hoisted like Jest
+- Spy: `vi.spyOn(obj, 'method')`
+- Timers: `vi.useFakeTimers()` / `vi.advanceTimersByTime(ms)`
+- Clear: `vi.clearAllMocks()` / `vi.resetAllMocks()` / `vi.restoreAllMocks()`
+- Snapshot: `expect(val).toMatchSnapshot()` — same as Jest
+
+## Mock Patterns
+```ts
+vi.mock('./dep.js', () => ({
+  myFn: vi.fn().mockReturnValue('mocked'),
+}));
+
+// Reset per test
+beforeEach(() => {
+  vi.clearAllMocks();
+  // re-set implementations after clear
+});
+```
+
+## Inline vs Config Mocks
+- `vi.mock()` in test file — hoisted, file-scoped
+- `__mocks__/` directory — auto-mock (same as Jest convention)
+- `vi.hoisted()` — declare variables used in `vi.mock()` factory
+
+## Key Differences from Jest
+- `vi` namespace instead of `jest` global
+- Native ESM — no `.js` extension issues in tests
+- `vi.stubEnv('KEY', 'val')` for env vars (cleaner than `process.env` mutation)
+- `--reporter=verbose` for detailed output
+- `vitest bench` for benchmarks (built-in, not separate tool)
+
+## Gotchas
+- `vi.mock()` factory can't reference outer variables unless via `vi.hoisted()`
+- `vi.clearAllMocks()` resets calls + implementations (same gotcha as Jest)
+- `--pool=forks` vs `--pool=threads` — forks for better isolation, threads for speed
+- SQLite tests: use `:memory:` or temp file, not shared DB (parallel execution)