Add artifact source previews

Docs audit: fix outdated references (PostgreSQL, Vue client, profiles, tools) ...

- architecture.md: SQLite → PostgreSQL + pgvector
- README.md: vanilla JS → Vue 3 + Pinia, remove smart_home, update temps
- profiles.md: remove smart_home, add discuss, update temperatures
- tools.md: add missing built-in tools, update user tools list
- sessions.md: fix outdated references
- NAVI.md: sync with current stack
- persona.txt: update self-extension and content_publish guidance
- content_publish.md manual: reflect session_dir-based no-copy design
- content_store.py & content_publish.py: inline with docs

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Add content_publish manual and improve tool description ...

- Create manuals/content_publish.md with full usage guide,
  internal mechanics, supported types, and best practices
- Update ContentPublishTool description with usage guidelines
  and examples in the tool schema
- All tests pass (150 backend + 47 webclient)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Rework content_publish: files live in session_dir, no copying ...

content_publish now registers existing session files for inline viewing
instead of copying them to navi/content/<uuid>/. This makes files
editable by the agent and immediately visible to the user via the
stable URL /sessions/{id}/files/{filename}.

- content_store.publish() → registers metadata, no shutil.copy2
- content_store.delete_content() → removes DB record only (file stays
  in session_dir; cleaned up by session lifecycle)
- content_store.cleanup_old() → deletes stale DB records
- ContentPublishTool:
  - accepts 'filename' instead of 'path'
  - looks up file in uploads/sessions/<id>/
  - returns clear error if file not found with instructions
  - includes full local path in output for future editing
- Added unique index on (session_id, filename) for idempotent re-publish
- Removed /content static mount from main.py (endpoint still works
  for legacy files; new files use /sessions/{id}/files/)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Add content hosting system with inline viewers ...

Backend:
- Add navi/content/ directory for published files
- Add content_store.py with publish/list/delete/cleanup functions
- Add content_publish tool for publishing files as viewable content
- Add /content static file mount in main.py
- Add /content-viewers mount for viewer pages
- Extend ToolEvent with metadata field
- Forward metadata through websocket tool_call events
- Update Agent to include metadata in ToolEvent

Frontend:
- Add ContentCard.vue component for displaying published content
- Add viewer pages: stl.html (Three.js), svg.html, html.html, pdf.html
- Update AssistantMessage.vue to render ContentCard for content_publish
- Update chat store to preserve metadata in tool cards
- Update websocket protocol docs with metadata field

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>