feat: add FastAPI web service wrapper

- Create REST API with endpoints for single and batch analysis
- Add async job support for long-running batch operations
- Implement job status tracking and listing endpoints
- Add 9 tests for API endpoints
- Update requirements.txt with fastapi, uvicorn, httpx
- Document API usage in README

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

requirements.txt

@@ -6,3 +6,6 @@ pytest
 pytest-mock
 openai
 psycopg2-binary
+fastapi
+uvicorn[standard]
+httpx