feat(api): implement OpenAPI/REST API for file conversions

- Add comprehensive REST API at /api/v1 with modular structure
- Implement authentication endpoints (register, login, logout, me)
- Add converter listing and format discovery endpoints
- Create job management and file download endpoints
- Add health check endpoint for monitoring
- Set up CORS support for browser-based API clients
- Create API middleware for JWT authentication
- Add environment variables for API configuration
- Include comprehensive API documentation and test script

Infrastructure:
- Enhanced CI/CD workflow for custom Docker registries
- Docker Compose setup with dev, prod, and monitoring profiles
- Claude.ai integration files for development workflow
- Environment-based configuration with .env.development

Known limitations:
- JWT authentication context needs fixing (using ALLOW_UNAUTHENTICATED=true)
- Swagger UI temporarily disabled due to composition error
- File upload endpoint needs multipart/form-data support

The API code is isolated in src/api/ directory to maintain separation
from the existing codebase, making it easy to maintain or contribute back.

IMPLEMENTATION_SUMMARY.md

@@ -0,0 +1,120 @@
+# ConvertX OpenAPI Implementation Summary
+
+## ✅ Completed Features
+
+### 1. Project Setup
+- **CLAUDE.md**: Complete codebase documentation
+- **Slash Commands**: `/commit`, `/pr`, `/test`, `/build` helpers
+- **Environment Configuration**: `.env.development` with API settings
+
+### 2. CI/CD Enhancements
+- **docker-publish-custom.yml**: Supports custom Docker registries
+- **docker-compose.yml**: Multi-profile setup (dev, prod, monitoring)
+- **Registry Configuration**: Environment variable based registry selection
+
+### 3. API Implementation
+- **Base Structure**: `/api/v1` endpoints with modular organization
+- **Health Check**: `/api/v1/health` - System status monitoring
+- **Authentication**: 
+  - `POST /api/v1/auth/register` - User registration
+  - `POST /api/v1/auth/login` - JWT token generation
+  - `GET /api/v1/auth/me` - Current user info
+  - `POST /api/v1/auth/logout` - Session cleanup
+- **Converters**:
+  - `GET /api/v1/converters` - List all converters
+  - `GET /api/v1/converters/:name` - Converter details
+  - `GET /api/v1/converters/formats/:format` - Find converters by format
+- **Jobs**:
+  - `GET /api/v1/jobs` - List user jobs
+  - `GET /api/v1/jobs/:id` - Job details
+  - `DELETE /api/v1/jobs/:id` - Delete job
+- **Files**:
+  - `GET /api/v1/files/:jobId` - List job files
+  - `GET /api/v1/files/:jobId/:fileName` - Download file
+- **Conversions**:
+  - `POST /api/v1/conversions` - Start conversion (partial implementation)
+
+### 4. Documentation & Testing
+- **API.md**: Complete API documentation
+- **test-api.sh**: Automated API testing script
+- **CORS**: Full CORS support for browser-based clients
+
+## 🚧 Known Issues & Limitations
+
+### 1. Authentication Context
+- JWT verification in middleware needs fixing
+- Currently requires `ALLOW_UNAUTHENTICATED=true` for testing
+- User context not properly passed to route handlers
+
+### 2. File Upload
+- Conversion endpoint expects pre-uploaded files
+- Multipart file upload not yet implemented
+- Need to integrate with existing upload logic
+
+### 3. Swagger/OpenAPI
+- Swagger UI disabled due to Elysia composition error
+- OpenAPI spec generation needs debugging
+- Alternative: Manual API documentation provided
+
+## 🔮 Next Steps
+
+### Phase 2: Core Functionality
+1. Fix JWT authentication middleware
+2. Implement multipart file upload
+3. Complete conversion endpoint with actual file processing
+4. Add progress tracking via SSE or WebSockets
+
+### Phase 3: Enhanced Features
+1. API key authentication
+2. Rate limiting implementation
+3. Webhook notifications
+4. Batch conversion support
+
+### Phase 4: Production Ready
+1. Re-enable Swagger UI
+2. Add comprehensive error handling
+3. Implement request/response logging
+4. Performance optimization
+5. API versioning strategy
+
+## 📝 Usage
+
+### Development
+```bash
+# Install dependencies
+bun install
+
+# Start with API enabled
+export $(cat .env.development | xargs) && bun run dev
+
+# Test API
+./test-api.sh
+```
+
+### Docker
+```bash
+# Development with hot reload
+docker compose --profile dev up
+
+# Production
+docker compose up convertx
+```
+
+## 🔧 Configuration
+
+Key environment variables:
+- `API_ENABLED=true` - Enable API endpoints
+- `ALLOW_UNAUTHENTICATED=true` - Allow anonymous access (dev only)
+- `JWT_SECRET` - Secret for JWT signing
+- `API_RATE_LIMIT` - Requests per window
+- `API_RATE_WINDOW` - Rate limit time window
+
+## 🏗️ Architecture Notes
+
+- API code isolated in `src/api/` directory
+- Minimal changes to existing codebase
+- Reuses existing converter logic
+- Compatible with current database schema
+- Can be disabled via environment variable
+
+The foundation is solid and ready for the remaining features to be implemented in subsequent phases.