fix(deploy): run uvicorn from backend/ and health-check /api/health

Dockerfile

@@ -35,7 +35,8 @@ EXPOSE 8000
 
 # Health check
 HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
-    CMD curl -f http://localhost:8000/health || exit 1
+    CMD curl -f http://localhost:8000/api/health || exit 1
 
-# Run FastAPI server with static file serving
+# Run from the backend package dir so `app.main:app` imports correctly
+WORKDIR /app/backend
 CMD ["python", "-m", "uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]