docs: Clarify extension terminology and dev server limitations (#5042)

* docs: Clarify extension terminology and dev server limitations

* docs: removed unecessary callout to extension docs in main readme, in favor of the contributions.md

* docs: remove key points

* docs: change docs structure for better semantics and extensibility

* docs: add warning emoji

* docs: remove mention of 3D core extensions

* docs: add feedback in

CONTRIBUTING.md

@@ -61,8 +61,6 @@ Run `npm run prepare` to install Git pre-commit hooks. Currently, the pre-commit
 
 ### Dev Server
 
-Note: The dev server will NOT load any extension from the ComfyUI server. Only core extensions will be loaded.
-
 - Start local ComfyUI backend at `localhost:8188`
 - Run `npm run dev` to start the dev server
 - Run `npm run dev:electron` to start the dev server with electron API mocked
@@ -89,6 +87,10 @@ After you start the dev server, you should see following logs:
 Make sure your desktop machine and touch device are on the same network. On your touch device,
 navigate to `http://<server_ip>:5173` (e.g. `http://192.168.2.20:5173` here), to access the ComfyUI frontend.
 
+> ⚠️ IMPORTANT:
+The dev server will NOT load JavaScript extensions from custom nodes. Only core extensions (built into the frontend) will be loaded. This is because the shim system that allows custom node JavaScript to import frontend modules only works in production builds. Python custom nodes still function normally. See [Extension Development Guide](docs/extensions/development.md) for details and workarounds. And See [Extension Overview](docs/extensions/README.md) for extensions overview.
+
+
 ## Development Workflow
 
 ### Architecture Decision Records