docs: AI chat architecture + fix pre-existing build errors
Update docs/ARCHITECTURE.md with:
- AI Chat system architecture (context picker, streaming, MCP)
- WebSocket bridge protocol
- New files listing and data flow diagrams
- Updated tech stack table
Update mock-tauri.ts with richer AI chat mock responses
(context-aware summarize, expand, grammar responses).
Fix pre-existing TypeScript build errors:
- Add missing snippet/relationships to test VaultEntry fixtures
- Fix string|null → string type mismatches in Sidebar, NoteList, Inspector
- Remove unused imports (cn in Editor, AIChatPanel in App)
- Fix tryParseMarkdownToBlocks Promise cast
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
bca6b3c8e8