docs: fix two module guide snippets that do not work as written

The dock handle example used ctx outside onDevtoolsReady, and the RPC
example broadcast once from devtools:ready, which runs before any client
is connected, so the message never arrived. Broadcast on a change instead.

Author: antfubot

docs/content/2.module/0.guide.md

@@ -46,8 +46,10 @@ Set `category` (`app`, `analyze`, `server`, `modules`, `documentation`, `advance
 `register()` returns a handle to patch the entry later, for example to show a badge:
 
 ```ts
-const entry = ctx.docks.register({ id: 'my-module', /* ... */ })
-entry.update({ badge: '3' })
+onDevtoolsReady((ctx) => {
+  const entry = ctx.docks.register({ id: 'my-module', /* ... */ })
+  entry.update({ badge: '3' })
+})
 ```
 
 Learn more about [DevTools Utility Kit](/module/utils-kit).
@@ -112,9 +114,11 @@ export default defineNuxtModule({
         },
       })
 
-      // call client RPC functions
-      // since there might be multiple clients connected, `broadcast` calls all of them
-      rpc.broadcast({ method: 'show-notification', args: ['Hello from My Module!'], event: true })
+      // call client RPC functions when something changes; `broadcast` reaches
+      // every connected client (none are connected yet when this hook runs)
+      nuxt.hook('builder:watch', (_event, path) => {
+        rpc.broadcast({ method: 'show-notification', args: [`${path} changed`], event: true })
+      })
     })
   },
 })