fix(security): apply two findings from sharing security review

- get_document: strip extracted_text for share recipients (T-04-04-03 consistency)
- ShareModal: emit 'unshared' when last recipient is revoked; DocumentCard clears is_shared badge

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

frontend/src/components/documents/DocumentCard.vue

@@ -85,6 +85,7 @@
       v-if="showShareModal"
       :doc="doc"
       @close="showShareModal = false"
+      @unshared="doc.is_shared = false"
     />
   </div>
 </template>

frontend/src/components/sharing/ShareModal.vue

@@ -125,7 +125,7 @@ const props = defineProps({
   },
 })
 
-const emit = defineEmits(['close'])
+const emit = defineEmits(['close', 'unshared'])
 
 const docsStore = useDocumentsStore()
 
@@ -202,6 +202,7 @@ async function handleRevoke(shareId) {
 
   try {
     await docsStore.revokeShare(shareId)
+    if (shares.value.length === 0) emit('unshared', props.doc.id)
   } catch (e) {
     // Re-add on failure
     if (removed && removedIdx !== -1) {