Add node-serve setup hook

[mjackson]

Adds a synchronous setup(app) option to serve() for configuring native uWebSockets.js features before node-serve registers its Fetch fallback and starts listening. Fixes #11313.

• Passes the created uWS.TemplatedApp to setup before app.any("/*", ...), then surfaces setup errors synchronously without starting a listener.
• Covers native WebSocket routes, connection filters, normal Fetch fallback behavior, and setup failure behavior in node-serve tests.
• Documents WebSocket and filter usage, including uWS route pattern differences from Remix route-pattern.

serve(handler, {
  setup(app) {
    app.ws("/ws/chat", {
      open(ws) {
        ws.subscribe("chat")
      },
      message(ws, message, isBinary) {
        ws.publish("chat", message, isBinary)
      },
    })
  },
})

[github-actions]

Preview Build Available

A preview build has been created for this PR. You can install it using:

pnpm install "remix-run/remix#preview/pr-11315&path:packages/remix"

This preview build will be updated automatically as you push new commits.

[github-actions]

The preview branch preview/pr-11315 has been deleted now that this PR is merged/closed.