feat: Return door state as JSON

Co-authored-by: aider (gemini/gemini-2.5-pro-preview-05-06) <aider@aider.chat>

server.py

@@ -191,7 +191,7 @@ async def handle_root(request):
 async def handle_state(request):
     """Handler for the /state GET request."""
     state = get_derived_state()
-    return web.Response(text=state)
+    return web.json_response({'door': [state]})
 
 async def on_startup(app):
     """Actions to perform on application startup."""