feat: Phase 3 — web dashboard, testing, and CI/CD

- Remove multi-marketplace from Phase 3
- Add FastAPI web UI on port 8766 with basic auth
- Add 6 Jinja2 templates (dashboard, keywords, users, ads, stats)
- Add pytest test suite (45 tests, 49% coverage)
- Add GitHub Actions CI/CD workflow
- Update docker-compose.yml to expose web UI port
- Update Dockerfile to include tests

worker/requirements.txt

@@ -3,3 +3,11 @@ asyncpg==0.30.0
 httpx==0.27.2
 aiohttp>=3.9,<4
 python-dotenv==1.0.1
+fastapi==0.115.0
+uvicorn==0.30.0
+jinja2==3.1.4
+
+# Test dependencies
+pytest==8.3.0
+pytest-asyncio==0.24.0
+flake8==7.1.0