Annotations: Share the inspector across Studio and CLI

[shaunandrews]

Related issues

• Related to STU-2183
• Stacked on Agentic UI: Add multi-note annotation sessions #4521

How AI was used in this PR

AI helped extract the shared inspector and add parity tests. The resulting behavior and diff were reviewed manually.

Proposed Changes

• Use one annotation inspector in Studio and the standalone CLI instead of maintaining two implementations.
• Give CLI annotations the same multi-note save, continue, and send workflow introduced for Studio.
• Preserve saved notes when users stop annotating, matching the behavior merged in Agentic UI: Add multi-note annotation sessions #4521.
• Keep layered-element selection and the draggable composer consistent across both surfaces.
• Authenticate messages between the Studio host and preview with a per-session token.

⚠️ Visual change: needs human review in light + dark mode.

Testing Instructions

1. Run npm run cli:build.
2. Run node apps/cli/dist/cli/main.mjs code, then enter /annotate.
3. Add and save multiple notes on the current page, then send them together.
4. In Studio, confirm the same single-page multi-note flow still works.
5. Automated: npm run typecheck, npm run cli:build, and 41 focused inspector/preview tests.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?