feat(06.2-02): frontend — is_shared badge fix + permission dropdown + View/Edit toggle

- DocumentCard.vue: fix Shared pill to read doc.is_shared (was doc.share_count > 0)
- ShareModal.vue: add permission select between handle input and submit button
- ShareModal.vue: replace static "view" span with View/Edit toggle group per share row
- ShareModal.vue: add handlePermissionChange with optimistic update + rollback on error
- documents.js: update shareDocument(docId, handle, permission='view') signature
- documents.js: add updateSharePermission(shareId, permission) action
- api/client.js: pass permission in createShare POST body
- api/client.js: add updateSharePermission PATCH helper

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

frontend/src/api/client.js

@@ -328,11 +328,19 @@ export function moveDocument(docId, folderId) {
 
 // ── Shares ────────────────────────────────────────────────────────────────────
 
-export function createShare(docId, recipientHandle) {
+export function createShare(docId, recipientHandle, permission = 'view') {
   return request('/api/shares', {
     method: 'POST',
     headers: { 'Content-Type': 'application/json' },
-    body: JSON.stringify({ document_id: docId, recipient_handle: recipientHandle }),
+    body: JSON.stringify({ document_id: docId, recipient_handle: recipientHandle, permission }),
+  })
+}
+
+export function updateSharePermission(shareId, permission) {
+  return request(`/api/shares/${shareId}`, {
+    method: 'PATCH',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ permission }),
   })
 }