feat(admin-web): add 404 page for unknown routes

Unknown URLs previously rendered a blank page. Add a catch-all route
under AppShell that shows the requested path plus back / workspace
actions, with zh-CN and en-US copy.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/admin-web/src/router/index.ts

@@ -262,6 +262,16 @@ const router = createRouter({
             navKey: '/account/ai-points',
           },
         },
+        {
+          path: ':pathMatch(.*)*',
+          name: 'not-found',
+          component: () => import('@/views/NotFoundView.vue'),
+          meta: {
+            titleKey: 'route.notFound.title',
+            descriptionKey: 'route.notFound.description',
+            navKey: null,
+          },
+        },
       ],
     },
   ],