fix(useOrder): use VisibilityService.registerService (not onVisible/onHidden)

VisibilityService exposes `registerService(name, onResume, onPause)`
returning an unregister fn, not the `onVisible(cb)` / `onHidden(cb)`
shape I'd invented. OrderStatusPage was throwing
'visibility.onVisible is not a function' on every mount.

Rewire useOrder to register a (onResume, onPause) pair:
  onResume → immediate refetch + restart polling if status is
             non-terminal (useful for mobile where polling
             pauses during background)
  onPause  → stop polling to save battery while hidden
The returned unregister fn is called from onScopeDispose, same as
before. Also fixed the related TS narrowing on order.value.status
via the same Order|null cast already used elsewhere in this file.

Verified vue-tsc -b clean.

src/modules/restaurant/composables/useOrder.ts

@@ -19,6 +19,7 @@ import {
   SERVICE_TOKENS,
 } from '@/core/di-container'
 import appConfig from '@/app.config'
+import type { VisibilityService } from '@/core/services/VisibilityService'
 import type { RestaurantAPI } from '../services/RestaurantAPI'
 import type {
   Order,
@@ -42,10 +43,9 @@ export interface UseOrderReturn {
 
 export function useOrder(orderId: Ref<string> | string): UseOrderReturn {
   const api = injectService<RestaurantAPI>(SERVICE_TOKENS.RESTAURANT_API)
-  const visibility = tryInjectService<{
+  const visibility = tryInjectService<VisibilityService>(
-    onVisible: (cb: () => void) => () => void
+    SERVICE_TOKENS.VISIBILITY_SERVICE
-    onHidden: (cb: () => void) => () => void
+  )
-  }>(SERVICE_TOKENS.VISIBILITY_SERVICE)
 
   const pollMs =
     (
@@ -60,7 +60,7 @@ export function useOrder(orderId: Ref<string> | string): UseOrderReturn {
   const error = ref<Error | null>(null)
 
   let timer: ReturnType<typeof setInterval> | null = null
-  let unsubVisible: (() => void) | null = null
+  let unregisterVisibility: (() => void) | null = null
 
   function targetId(): string {
     return typeof orderId === 'string' ? orderId : orderId.value
@@ -105,13 +105,25 @@ export function useOrder(orderId: Ref<string> | string): UseOrderReturn {
   }
 
   // Refetch immediately when the tab becomes visible again — useful
-  // for mobile where polling pauses during background.
+  // for mobile where polling pauses during background. The
+  // VisibilityService takes (name, onResume, onPause) and returns
+  // an unregister fn.
   if (visibility) {
-    unsubVisible = visibility.onVisible(() => {
+    unregisterVisibility = visibility.registerService(
-      fetchOnce().then(() => {
+      `useOrder-${typeof orderId === 'string' ? orderId : 'ref'}`,
-        if (!isTerminal(order.value?.status)) startPolling()
+      async () => {
-      })
+        await fetchOnce()
-    })
+        if (
+          !isTerminal((order.value as Order | null)?.status)
+        ) {
+          startPolling()
+        }
+      },
+      async () => {
+        // pause polling while hidden — saves battery on mobile
+        stopPolling()
+      }
+    )
   }
 
   watch(
@@ -129,7 +141,7 @@ export function useOrder(orderId: Ref<string> | string): UseOrderReturn {
 
   onScopeDispose(() => {
     stopPolling()
-    unsubVisible?.()
+    unregisterVisibility?.()
   })
 
   return {