Migrate storage to PostgreSQL with SQLite fallback; misc fixes ...

- Add PgSessionStore (asyncpg pool) and PgMemoryStore replacing aiosqlite
- Keep SqliteSessionStore + SqliteMemoryStore for zero-dependency quick start
- Selection logic in deps.py: DATABASE_URL set → PG, else → SQLite
- Add asyncpg>=0.29 to dependencies; add DATABASE_URL / DB_PATH to config
- Add RESPONSE HYGIENE rule to persona: never echo tool output or plan state
- Add developer profile user tools: weather, internal_monitor
- Update README: developer profile, DB section, current tool/profile state

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

self edited

Add project docs, tool manuals, and initial user tools ...

- CLAUDE.md: comprehensive project reference for Claude Code sessions
- manuals/write_tool.md: full format reference with working example
- tools/_template.py: canonical module-level tool format
- tools/enabled.json: auto-include list (get_current_datetime, user_notes)
- get_current_datetime, user_notes: first Navi-written tools

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>