Add visual annotation browser with Agentation

[lezama]

Summary

Adds /annotate skill to Studio Code. Users type /annotate, a browser opens with the Agentation annotation toolbar, they click elements and leave feedback, and the agent reads those annotations and makes changes.

Tested end-to-end: user annotated "make this red", "change this to H2" → agent read annotations, applied changes via Global Styles custom CSS and WP-CLI.

Alternative approach to the custom element picker in #2936 — instead of building a custom UI, this injects Agentation's React toolbar into a Playwright browser using esm.sh CDN with ?deps= pinning for a single React instance.

How it works

1. agentation-mcp bundled as dependency — launches HTTP (localhost:4747) + MCP servers
2. /annotate skill clears old annotations, opens headed Playwright browser via open_annotation_browser tool
3. Agentation React component injected via dynamic import() from esm.sh CDN
4. User clicks elements, adds feedback in the browser
5. Agent reads annotations with agentation_get_all_pending (CSS selectors, computed styles, text)
6. Agent makes WordPress changes (Global Styles CSS, template overrides, WP-CLI) and resolves annotations

Changes

• apps/cli/ai/agentation-inject.ts (new) — Opens headed Playwright browser, injects Agentation via esm.sh dynamic imports
• apps/cli/ai/tools.ts — New open_annotation_browser tool
• apps/cli/ai/plugin/skills/annotate/SKILL.md (new) — /annotate skill with guided workflow and WordPress-native change patterns
• apps/cli/ai/slash-commands.ts — Register /annotate command
• apps/cli/ai/agent.ts — Agentation MCP server added alongside Studio tools
• apps/cli/package.json — agentation-mcp dependency

Testing

1. npm install && npm run cli:build
2. node apps/cli/dist/cli/main.mjs code
3. Select a running site, type /annotate
4. Click the circle icon (bottom-right), click elements, add feedback
5. Type "done" — agent reads and applies changes

Quality gates

• ESLint: pass
• TypeScript: pass
• Tests: 72/72 pass
• End-to-end: annotations synced and applied to WordPress site