feat(scan+sharing): polish rapid scan feedback and invite UX states

- Add scanner status bar with real-time state (ready/scanning/saved)
- Add success pulse styling after accepted detection for faster repeated scans
- Keep scanner in uninterrupted loop while giving clear visual confirmation
- Add invite busy state in manage collection to prevent duplicate submits
- Improve collaborative management responsiveness with explicit inviting state

lib/scanner_screen.dart

@@ -24,6 +24,8 @@ class _ScannerScreenState extends State<ScannerScreen> {
   bool _isBusy = false;
   bool _cameraReady = false;
   String? _lastDetected;
+  bool _scanAccepted = false;
+  String _statusText = 'Ready to scan';
 
   // Matches typical Hot Wheels model IDs: 2–5 uppercase letters followed by
   // 2–4 digits, e.g. JKF21, HCV73, GRX33, FYD83.
@@ -67,7 +69,10 @@ class _ScannerScreenState extends State<ScannerScreen> {
   Future<void> _captureAndScan() async {
     if (_isBusy || _cameraController == null || !_cameraController!.value.isInitialized) return;
 
-    setState(() => _isBusy = true);
+    setState(() {
+      _isBusy = true;
+      _statusText = 'Scanning…';
+    });
 
     try {
       final xFile = await _cameraController!.takePicture();
@@ -118,8 +123,16 @@ class _ScannerScreenState extends State<ScannerScreen> {
       ScaffoldMessenger.of(context).showSnackBar(
         SnackBar(content: Text('Scan error: $e'), backgroundColor: Colors.red),
       );
+      setState(() => _statusText = 'Scan failed, try again');
     } finally {
-      if (mounted) setState(() => _isBusy = false);
+      if (mounted) {
+        setState(() {
+          _isBusy = false;
+          if (_statusText == 'Scanning…') {
+            _statusText = 'Ready to scan';
+          }
+        });
+      }
     }
   }
 
@@ -134,7 +147,15 @@ class _ScannerScreenState extends State<ScannerScreen> {
       if (!mounted) return;
 
       if (keepScanning) {
-        setState(() => _lastDetected = null);
+        setState(() {
+          _lastDetected = null;
+          _scanAccepted = true;
+          _statusText = 'Saved. Ready for next scan';
+        });
+        Future<void>.delayed(const Duration(milliseconds: 650), () {
+          if (!mounted) return;
+          setState(() => _scanAccepted = false);
+        });
       } else {
         Navigator.of(context).pop();
       }
@@ -167,6 +188,22 @@ class _ScannerScreenState extends State<ScannerScreen> {
       ),
       body: Column(
         children: [
+          Container(
+            width: double.infinity,
+            padding: const EdgeInsets.symmetric(horizontal: 14, vertical: 8),
+            color: _scanAccepted
+                ? AppColors.success.withValues(alpha: 0.12)
+                : Colors.black.withValues(alpha: 0.55),
+            child: Text(
+              _statusText,
+              textAlign: TextAlign.center,
+              style: TextStyle(
+                color: _scanAccepted ? AppColors.success : Colors.white,
+                fontSize: 12,
+                fontWeight: FontWeight.w600,
+              ),
+            ),
+          ),
           // ── Camera preview ──
           Expanded(
             child: _cameraReady
@@ -192,7 +229,10 @@ class _ScannerScreenState extends State<ScannerScreen> {
                           height: 100,
                           decoration: BoxDecoration(
                             border: Border.all(
-                              color: AppColors.orange.withValues(alpha: 0.8),
+                              color: (_scanAccepted
+                                      ? AppColors.success
+                                      : AppColors.orange)
+                                  .withValues(alpha: 0.9),
                               width: 2.5,
                             ),
                             borderRadius: BorderRadius.circular(16),

lib/screens/manage_collection_screen.dart

@@ -18,6 +18,7 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
   late Collection _collection;
   List<CollectionMember> _members = [];
   bool _isLoading = true;
+  bool _isInviting = false;
 
   @override
   void initState() {
@@ -128,6 +129,7 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
   }
 
   Future<void> _inviteMember() async {
+    if (_isInviting) return;
     final emailCtrl = TextEditingController();
 
     final result = await showDialog<bool>(
@@ -192,6 +194,7 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
     }
 
     try {
+      setState(() => _isInviting = true);
       await CollectionService.inviteByEmail(
         collectionId: _collection.id,
         email: email,
@@ -200,6 +203,8 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
       _loadMembers();
     } catch (e) {
       showGlobalSnackBar('$e', isError: true);
+    } finally {
+      if (mounted) setState(() => _isInviting = false);
     }
   }
 
@@ -347,9 +352,9 @@ class _ManageCollectionScreenState extends State<ManageCollectionScreen> {
                 const Spacer(),
                 if (_collection.isOwner)
                   TextButton.icon(
-                    onPressed: _inviteMember,
+                    onPressed: _isInviting ? null : _inviteMember,
                     icon: const Icon(Icons.person_add, size: 18),
-                    label: const Text('Invite'),
+                    label: Text(_isInviting ? 'Inviting…' : 'Invite'),
                   ),
               ],
             ),