feat(scanner): add auto-scan cadence with pause/resume controls

- Add periodic auto-capture loop for uninterrupted scanner workflow
- Start auto-scan after camera init and stop cleanly on dispose
- Gate scans by busy/camera-ready state to avoid overlapping captures
- Add AUTO ON/OFF toggle in scanner status bar
- Keep manual capture path available as fallback

lib/scanner_screen.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:io';
 
 import 'package:flutter/material.dart';
@@ -37,6 +38,8 @@ class _ScannerScreenState extends State<ScannerScreen> {
   bool _scanAccepted = false;
   String _statusText = 'Ready to scan';
   String? _activeCollectionId;
+  bool _autoScanEnabled = false;
+  Timer? _autoScanTimer;
 
   // Matches typical Hot Wheels model IDs: 2–5 uppercase letters followed by
   // 2–4 digits, e.g. JKF21, HCV73, GRX33, FYD83.
@@ -46,6 +49,7 @@ class _ScannerScreenState extends State<ScannerScreen> {
   void initState() {
     super.initState();
     _activeCollectionId = widget.activeCollectionId;
+    _autoScanEnabled = widget.onDetected != null;
     _textRecognizer = TextRecognizer();
     _initCamera();
   }
@@ -81,6 +85,22 @@ class _ScannerScreenState extends State<ScannerScreen> {
     await _cameraController!.initialize();
     if (!mounted) return;
     setState(() => _cameraReady = true);
+    _startAutoScanLoop();
+  }
+
+  void _startAutoScanLoop() {
+    _autoScanTimer?.cancel();
+    _autoScanTimer = Timer.periodic(const Duration(milliseconds: 1400), (_) {
+      if (!_autoScanEnabled || _isBusy || !_cameraReady || !mounted) return;
+      _captureAndScan();
+    });
+  }
+
+  void _toggleAutoScan() {
+    setState(() {
+      _autoScanEnabled = !_autoScanEnabled;
+      _statusText = _autoScanEnabled ? 'Auto scan enabled' : 'Auto scan paused';
+    });
   }
 
   /// Capture a photo, run OCR, and look for a Hot Wheels ID.
@@ -187,6 +207,7 @@ class _ScannerScreenState extends State<ScannerScreen> {
 
   @override
   void dispose() {
+    _autoScanTimer?.cancel();
     _cameraController?.dispose();
     _textRecognizer.close();
     super.dispose();
@@ -243,6 +264,9 @@ class _ScannerScreenState extends State<ScannerScreen> {
             color: _scanAccepted
                 ? AppColors.success.withValues(alpha: 0.12)
                 : Colors.black.withValues(alpha: 0.55),
+            child: Row(
+              children: [
+                Expanded(
                   child: Text(
                     _statusText,
                     textAlign: TextAlign.center,
@@ -253,6 +277,20 @@ class _ScannerScreenState extends State<ScannerScreen> {
                     ),
                   ),
                 ),
+                if (widget.onDetected != null)
+                  TextButton(
+                    onPressed: _isBusy ? null : _toggleAutoScan,
+                    style: TextButton.styleFrom(
+                      foregroundColor:
+                          _autoScanEnabled ? AppColors.success : Colors.white,
+                      minimumSize: const Size(0, 26),
+                      padding: const EdgeInsets.symmetric(horizontal: 10),
+                    ),
+                    child: Text(_autoScanEnabled ? 'AUTO ON' : 'AUTO OFF'),
+                  ),
+              ],
+            ),
+          ),
           // ── Camera preview ──
           Expanded(
             child: _cameraReady