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.

.claude/pr.md

@@ -0,0 +1,52 @@
+# Create Pull Request
+
+Please create a pull request with the following steps:
+
+1. **Ensure branch is up to date**:
+   - Check current branch with `git branch --show-current`
+   - Pull latest changes from main/master
+   - Push current branch to remote
+
+2. **Create PR using GitHub CLI** (`gh pr create`) with:
+   - Clear, descriptive title
+   - Comprehensive description including:
+     - What changes were made
+     - Why these changes were necessary
+     - How to test the changes
+     - Any breaking changes or migration notes
+
+3. **PR Template**:
+   ```markdown
+   ## Summary
+   Brief description of what this PR does.
+
+   ## Changes
+   - List of specific changes made
+   - Organized by component/feature
+
+   ## Testing
+   - [ ] Unit tests pass
+   - [ ] Integration tests pass
+   - [ ] Manual testing completed
+   - [ ] Documentation updated
+
+   ## Screenshots
+   (If applicable)
+
+   ## Breaking Changes
+   - List any breaking changes
+   - Migration instructions if needed
+
+   ## Related Issues
+   Closes #XXX
+   ```
+
+4. **Labels to consider**:
+   - `enhancement`: New features
+   - `bug`: Bug fixes
+   - `documentation`: Doc updates
+   - `api`: API-related changes
+   - `docker`: Container changes
+   - `dependencies`: Dependency updates
+
+Please analyze the current branch changes and create an appropriate PR.