Add artifact source previews

Improve content publishing UX

Docs audit: fix outdated references (PostgreSQL, Vue client, profiles, tools) ...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- sessions.md: fix outdated references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>