docs: add missing content from summary.md (API reference, Android app, file structure, LLM internals)

- docs/api-reference.md: complete REST API endpoint reference (~60+ routes)
- docs/android-app.md: Flutter companion app stack, architecture, feature status
- docs/architecture.md: detailed file-by-file reference for all backend services and frontend components
- docs/features.md: LLM pipeline internals (intent routing, tool loop, duplicate guards, image search, research pipeline), roadmap
- docs/development.md: full migration chain (0001–0026) with naming and caveats
- README.md: link to new api-reference and android-app docs

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

README.md

@@ -39,6 +39,8 @@ Go to **Settings → General** to pull an LLM model. `qwen3:8b` or `llama3.1:8b`
 | [Development](docs/development.md) | Dev workflow, CI/CD, migrations, release process |
 | [API Keys & MCP](docs/api-keys-and-mcp.md) | API key management and Fable MCP install guide |
 | [SSO / OAuth](docs/sso-oauth.md) | OIDC setup for Authentik, Keycloak, and other providers |
+| [API Reference](docs/api-reference.md) | All REST API endpoints |
+| [Android App](docs/android-app.md) | Flutter companion app architecture and feature status |
 | [Changelog](docs/changelog.md) | Development history |
 
 ## License