fix: eliminate shell syntax in git.run() across 8 remaining tools

[TerminalGravity]

Fixes #172

Problem

run() uses execFileSync('git', args) — no shell. 8 tools passed shell operators that silently broke.

Fix

• New src/lib/shell.ts for commands needing shell interpretation
• Array-arg run() calls for git commands
• Native Node.js fs replacing cat/wc/find
• In-JS filtering replacing grep/head/tail pipes

Tools: verify-completion, token-audit, session-handoff, audit-workspace, sharpen-followup, scope-work, enrich-agent-task, sequence-tasks

Build clean, 43/43 tests pass.

[TerminalGravity]

This is the cleanest approach to #172 — the new shell() helper in lib/shell.ts is the right abstraction for commands that genuinely need shell interpretation (like gh pr list with fallback, or tail -c), while everything else correctly moves to array-arg run() or native Node APIs.

A few things I like:

• hasCommand() using which via execFileSync instead of command -v through a shell — correct and portable
• Reading package.json and counting lines via fs instead of shelling out to cat/wc — way more reliable
• The shell() helper has good timeout handling and captures both stdout+stderr on non-zero exits (important for tsc)
• Slicing output in JS (.slice(-20)) instead of piping through tail

One minor note: enrich-agent-task.ts still references shellEscape in findRelatedTests (line ~53) but it's no longer needed there since you're building a RegExp, not a shell command. Won't break anything but it's dead logic — could clean it up.

This supersedes #195, #197, and #198 — let's close those once this lands. Ready to merge. 🚀

[TerminalGravity]

Closing — superseded by #204 which covers all remaining tools. Let's consolidate there.