docs: Restructure documentation with Bookstack-compatible hierarchy

- Organized docs into numbered shelf/book/chapter/page structure
- Created comprehensive README.md with project overview
- Added Getting Started book (quick start, installation, configuration)
- Added Development book (workflow, testing, type sharing)
- Added Architecture book (design principles, PDA-friendly patterns)
- Added API Reference book (conventions, authentication)
- Moved TYPE-SHARING.md to proper location
- Updated all cross-references in main README
- Created docs/README.md as master index
- Removed old QA automation reports
- Removed deprecated SETUP.md (content split into new structure)

Documentation structure follows Bookstack best practices:
- Numbered books: 1-getting-started, 2-development, 3-architecture, 4-api
- Numbered chapters and pages for ordering
- Clear hierarchy and navigation
- Cross-referenced throughout

Complete documentation available at: docs/README.md

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docs/4-api/README.md

@@ -0,0 +1,32 @@
+# API Reference
+
+Complete API documentation for Mosaic Stack backend.
+
+## Chapters
+
+1. **Conventions** — API design patterns, endpoints, and response formats
+2. **Authentication** — Auth endpoints and type definitions
+
+## API Standards
+
+- **REST Conventions:** Standard HTTP methods and status codes
+- **Type Safety:** All requests/responses typed via `@mosaic/shared`
+- **Error Handling:** Consistent error response format
+- **Authentication:** Bearer token via Authorization header
+
+## Base URL
+
+- **Development:** `http://localhost:3001`
+- **Production:** Configure via `NEXT_PUBLIC_APP_URL`
+
+## Authentication
+
+All authenticated endpoints require:
+```http
+Authorization: Bearer {session_token}
+```
+
+## Next Steps
+
+- Review **Architecture** for design context
+- Check **Development** for contributing guidelines