feat(10-09): add global keydown handler to App.vue — /, Escape, U, N shortcuts live

- Add routeViewRef = ref(null) and bind to <router-view ref="routeViewRef">
- Add onKeydown handler: guards INPUT/TEXTAREA/SELECT/contenteditable; routes / → focusSearch, Escape → clearSearch, U/u → triggerUpload, N/n → startNewFolder
- Chain document.addEventListener on onMounted, removeEventListener on onUnmounted
- Add double optional chaining (?.) in StorageBrowser.triggerUpload and focusSearch so stubs don't throw in tests
- 9 keyboard shortcut tests GREEN; full suite 190 passing 0 failures

frontend/src/App.vue

@@ -3,14 +3,14 @@
   <div v-else class="flex h-screen overflow-hidden">
     <AppSidebar />
     <main class="flex-1 overflow-y-auto">
-      <router-view />
+      <router-view ref="routeViewRef" />
     </main>
   </div>
   <ToastContainer />
 </template>
 
 <script setup>
-import { onMounted } from 'vue'
+import { ref, onMounted, onUnmounted } from 'vue'
 import { useRoute } from 'vue-router'
 import AppSidebar from './components/layout/AppSidebar.vue'
 import AuthLayout from './layouts/AuthLayout.vue'
@@ -19,5 +19,30 @@ import { useTopicsStore } from './stores/topics.js'
 
 const route = useRoute()
 const topicsStore = useTopicsStore()
-onMounted(() => topicsStore.fetchTopics())
+const routeViewRef = ref(null)
+
+function onKeydown(e) {
+  const tag = document.activeElement?.tagName
+  if (['INPUT', 'TEXTAREA', 'SELECT'].includes(tag) || document.activeElement?.isContentEditable) return
+
+  if (e.key === '/' && !e.ctrlKey && !e.metaKey) {
+    e.preventDefault()
+    routeViewRef.value?.focusSearch?.()
+  }
+  if (e.key === 'Escape') {
+    routeViewRef.value?.clearSearch?.()
+  }
+  if (e.key === 'u' || e.key === 'U') {
+    routeViewRef.value?.triggerUpload?.()
+  }
+  if (e.key === 'n' || e.key === 'N') {
+    routeViewRef.value?.startNewFolder?.()
+  }
+}
+
+onMounted(() => {
+  topicsStore.fetchTopics()
+  document.addEventListener('keydown', onKeydown)
+})
+onUnmounted(() => document.removeEventListener('keydown', onKeydown))
 </script>