fix(10): resolve CR-01 prop mutation + CR-02 double-shortcut on modal open

CR-01: DocumentCard.vue `@unshared="doc.is_shared = false"` mutated a
defineProps prop (readonly in Vue 3). Replace with a local `isShared` ref
watched against prop changes so the Shared pill hides correctly after revoke.

CR-02: App.vue keyboard handler fired U/N/Escape shortcuts even when a modal
was open (no input focused). Add `role="dialog"` guard so all shortcuts are
suppressed while any dialog is in the DOM.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/App.vue

@@ -30,6 +30,7 @@ function onOsFilesDropped(files) {
 function onKeydown(e) {
   const tag = document.activeElement?.tagName
   if (['INPUT', 'TEXTAREA', 'SELECT'].includes(tag) || document.activeElement?.isContentEditable) return
+  if (document.querySelector('[role="dialog"]')) return
 
   if (e.key === '/' && !e.ctrlKey && !e.metaKey) {
     e.preventDefault()

frontend/src/components/documents/DocumentCard.vue

@@ -36,7 +36,7 @@
         </div>
 
         <!-- Shared indicator pill -->
-        <div v-if="doc.is_shared" class="mt-2">
+        <div v-if="isShared" class="mt-2">
           <span class="bg-indigo-50 text-indigo-600 text-xs font-medium px-2 py-1 rounded-full">Shared</span>
         </div>
 
@@ -83,7 +83,7 @@
       v-if="showShareModal"
       :doc="doc"
       @close="showShareModal = false"
-      @unshared="doc.is_shared = false"
+      @unshared="isShared = false"
     />
   </div>
 
@@ -113,7 +113,7 @@
 </template>
 
 <script setup>
-import { ref, computed, onMounted, onUnmounted } from 'vue'
+import { ref, computed, watch, onMounted, onUnmounted } from 'vue'
 import AppIcon from '../ui/AppIcon.vue'
 import { useTopicsStore } from '../../stores/topics.js'
 import { useFoldersStore } from '../../stores/folders.js'
@@ -128,6 +128,9 @@ const props = defineProps({
 
 const emit = defineEmits(['reclassified'])
 
+const isShared = ref(props.doc?.is_shared ?? false)
+watch(() => props.doc?.is_shared, v => { isShared.value = v ?? false })
+
 const topicsStore = useTopicsStore()
 const foldersStore = useFoldersStore()
 const showShareModal = ref(false)