feat: remove calendar and refine habits

backend/main.py

@@ -806,6 +806,8 @@ if static_dir.exists():
 
     @app.get("/{path:path}", include_in_schema=False)
     async def spa(path: str):
+        if path == "api" or path.startswith("api/"):
+            raise HTTPException(status_code=404, detail="Not Found")
         root = static_dir.resolve()
         target = (root / path).resolve()
         headers = {"Cache-Control": "no-cache, no-store, must-revalidate, max-age=0"}