Docs: actualize navi_code tool lists and key_tools ...

- docs/navi_code.md and docs/profiles.md now correctly list native tools,
  MCP navi-web tools, and excluded tools.
- image_view is documented as enabled for the agent (loads and describes
  images for the model, not shown to the user).
- web_search/http_request are documented as MCP navi-web tools, not native
  disabled tools.
- navi/profiles/navi_code/config.json: updated full_description.key_tools to
  match actual resolved tool names.

Tests: 459 passed, 1 skipped.

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

Navi Code: Phase 1 — terminal-first profile, default profile mechanism, env/persona, tests ...

- Add navi_code profile (terminal-first coding assistant)
- Add NAVI_DEFAULT_PROFILE_ID setting and POST /sessions default profile fallback
- Add persona_navi_code.txt and .env.navi_code.example
- Add docs/plan_navi_code.md phased plan
- Update tests to verify default-profile selection in no-auth mode

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