Add Ask AI to plan and annotate reviews

[backnotprop]

Summary

• Add Ask AI to plan review and annotate sessions with a shared document side chat and comment-popover Ask AI action.
• Mount the shared AI runtime across Bun plan/annotate/review servers and the Pi mirror, including long-lived SSE query handling.
• Add origin-aware provider defaults, per-origin provider persistence, and the first-run Ask AI announcement for annotated documents.
• Reuse the shared AI chat hook/icon path in code review and remove the old AI setup dialog.
• Update docs/tests for provider defaults, plan/annotate AI context, and Pi route/runtime parity.

Self-review notes

• Verified the plan/annotate implementation uses the same provider-agnostic AI endpoints as code review instead of a separate pipe.
• Checked that Ask AI chat history stays separate from approve/deny annotation output.
• Confirmed the notification follows the existing dismiss-once cookie pattern and reuses provider icon metadata.
• Fixed one self-review issue before commit: stale provider IDs in the compact provider bar now fall back to an available provider cleanly.

Verification

• PATH="$PWD/packages/ui/node_modules/.bin:$PATH" bun run typecheck
• bun test
• bun run build:hook
• Rebuilt local which plannotator binary and confirmed plannotator 0.19.20