fix: prevent invite role dropdown overflow

lib/screens/manage_collection_screen.dart

@@ -173,20 +173,34 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
                 ),
                 const SizedBox(height: 12),
                 DropdownButtonFormField<String>(
+                  isExpanded: true,
                   initialValue: inviteRole,
                   decoration: const InputDecoration(
                     labelText: 'Role',
                     prefixIcon: Icon(Icons.security_outlined),
                   ),
                   items: const [
-                    DropdownMenuItem(value: 'member', child: Text('Member (can add/copy/edit)')),
+                    DropdownMenuItem(value: 'member', child: Text('Member')),
-                    DropdownMenuItem(value: 'viewer', child: Text('Viewer (read-only)')),
+                    DropdownMenuItem(value: 'viewer', child: Text('Viewer')),
                   ],
                   onChanged: (value) {
                     if (value == null) return;
                     setSheetState(() => inviteRole = value);
                   },
                 ),
+                const SizedBox(height: 8),
+                Align(
+                  alignment: Alignment.centerLeft,
+                  child: Text(
+                    inviteRole == 'viewer'
+                        ? 'Viewer: read-only access.'
+                        : 'Member: can add, copy, edit, and remove cars.',
+                    style: const TextStyle(
+                      fontSize: 12,
+                      color: AppColors.textSecondary,
+                    ),
+                  ),
+                ),
               ],
             ),
           ),