Add VS Code quick actions for Wrap-up prompt shaping and full-depth override

[jsmestad]

What

Users should be able to quickly choose whether AI interactions prioritize fast completion or full-depth output from within the HeadsDown VS Code quick action menu.

Why

Default steering toward completion only works if users can override it easily when deeper thinking is needed. A fast, visible control increases adoption and prevents frustration from hidden automation.

Acceptance Criteria

1. Quick Actions includes a "Copy AI Wrap-up Brief" action that copies a concise shaping prompt to the clipboard when wrap-up is active.
2. Quick Actions includes a "Use Full Depth for this task" action that clearly communicates this is a temporary override for the next proposal/task.
3. The extension confirms action success with a user-visible notification.
4. If wrap-up is inactive, the Wrap-up brief action either hides or explains why it is unavailable.
5. Unit tests verify menu options, clipboard behavior, and override action handling.

Developer Notes

Approach: Add two new command paths under existing quick actions. Keep behavior lightweight for MVP: clipboard shaping plus explicit override intent signaling.

Steps:

1. Add quick action items and command handlers.
   • Files: src/extension.ts
2. Add helper for generating wrap-up brief text from availability guidance.
   • Files: src/extension.ts or new small helper module in src/
3. Add success/error notifications and fallback copy text.
   • Files: src/extension.ts
4. Add tests for action visibility and execution.
   • Files: test/* (quick action related tests)

Testing:

• Validate clipboard content for active wrap-up.
• Validate override action path and user notification.
• Validate inactive-state behavior.

[jsmestad]

Dependency note: this ticket depends on the shared Finish Today (Wrap-up Guidance) API/SDK contract in https://github.com/headsdownapp/heads_down/issues/812. Implementation should start after that contract lands (or behind feature-flagged SDK prerelease).