fix(06.2): resolve four sharing UX issues found in re-test UAT

- AccountView: remove hardcoded @ prefix so handle matches what share dialog expects
- documents store: set is_shared=true optimistically after successful share so badge shows without refetch
- GET /api/documents/{id}: allow recipients of an active share to view the document (was returning 404 for non-owners)
- ShareModal: move Share button to its own full-width row so it no longer overflows the input area

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

backend/api/documents.py

@@ -542,7 +542,18 @@ async def get_document(
         raise HTTPException(404, "Document not found")
 
     doc = await session.get(Document, uid)
-    if doc is None or doc.user_id != current_user.id:
+    if doc is None:
+        raise HTTPException(404, "Document not found")
+
+    if doc.user_id != current_user.id:
+        # Allow recipients of an active share to view the document
+        share_result = await session.execute(
+            select(Share).where(
+                Share.document_id == uid,
+                Share.recipient_id == current_user.id,
+            )
+        )
+        if share_result.scalar_one_or_none() is None:
             raise HTTPException(404, "Document not found")
 
     meta = await storage.get_metadata(session, doc_id)

frontend/src/components/sharing/ShareModal.vue

@@ -28,6 +28,7 @@
       </h2>
 
       <!-- Handle input row -->
+      <div class="flex flex-col gap-2">
         <div class="flex gap-2">
           <input
             v-model="handle"
@@ -44,12 +45,13 @@
             <option value="view">Can view</option>
             <option value="edit">Can edit</option>
           </select>
+        </div>
         <button
           @click="submitShare"
           :disabled="submitting || !handle.trim()"
-          class="bg-indigo-600 hover:bg-indigo-700 text-white text-sm px-4 py-2 rounded-lg disabled:opacity-50 transition-colors shrink-0"
+          class="w-full bg-indigo-600 hover:bg-indigo-700 text-white text-sm px-4 py-2 rounded-lg disabled:opacity-50 transition-colors"
         >
-          <span v-if="submitting" class="flex items-center gap-1.5">
+          <span v-if="submitting" class="flex items-center justify-center gap-1.5">
             <span class="animate-spin rounded-full border-2 border-current border-t-transparent w-3 h-3"></span>
             Sharing…
           </span>

frontend/src/stores/documents.js

@@ -157,7 +157,10 @@ export const useDocumentsStore = defineStore('documents', () => {
   }
 
   async function shareDocument(docId, recipientHandle, permission = 'view') {
-    try { return await api.createShare(docId, recipientHandle, permission) } catch (e) { throw e }
+    const result = await api.createShare(docId, recipientHandle, permission)
+    const doc = documents.value.find(d => d.id === docId)
+    if (doc) doc.is_shared = true
+    return result
   }
 
   async function revokeShare(shareId) {

frontend/src/views/AccountView.vue

@@ -9,7 +9,7 @@
         <h3 class="font-semibold text-gray-800 mb-4">Account information</h3>
         <div class="space-y-2 text-sm text-gray-700">
           <div><span class="text-gray-500">Email:</span> {{ authStore.user?.email }}</div>
-          <div><span class="text-gray-500">Username:</span> @{{ authStore.user?.handle }}</div>
+          <div><span class="text-gray-500">Username:</span> {{ authStore.user?.handle }}</div>
           <div class="flex items-center gap-2">
             <span class="text-gray-500">Role:</span>
             <span