feat(docker): add Docker Compose deployment for Dokploy

- backend/Dockerfile: Python 3.12-slim, uvicorn on port 8000
- frontend/Dockerfile: multi-stage Node build + nginx:alpine serve
- frontend/nginx.conf: proxy /api to backend, SPA routing for Vue Router
- docker-compose.yml: backend+frontend services with Traefik labels
- fix(cors): use settings.frontend_url instead of hardcoded localhost

Fixes Nixpacks detection failure (requirements.txt/package.json not at root).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -34,7 +34,7 @@ app = FastAPI(title=settings.app_name)
 # CORS middleware
 app.add_middleware(
     CORSMiddleware,
-    allow_origins=["http://localhost:5173"],  # Frontend dev server
+    allow_origins=[settings.frontend_url, "http://localhost:5173"],
     allow_credentials=True,
     allow_methods=["*"],
     allow_headers=["*"],