Add frontend debug mode gate

.env.example

@@ -173,6 +173,10 @@ VITE_SCENE_IMAGE_REQUEST_TIMEOUT_MS="150000"
 # Keep this off by default for cleaner logs.
 VITE_LLM_DEBUG_LOG="false"
 
+# Optional: global frontend debug mode. When empty, it follows Vite dev mode.
+# Set to "true" to expose local diagnostic panels, or "false" to hide them.
+VITE_DEBUG_MODE=""
+
 # Optional: official VikingDB credentials for regenerating build-tag similarities
 # with the Python embedding script. The script auto-loads `.env.local` and uses
 # the fixed `bge-large-zh` embedding model.