feat: improved receipt recognition, batch product add, and scan UX

- Rewrite receipt OCR prompt: completes truncated names, preserves fat%
  and flavour attributes, extracts weight/volume from line, infers
  typical package sizes for solid goods with quantity_confidence field
- Add quantity_confidence to RecognizedItem, EnrichedItem, and
  ProductJobResultItem; propagate through item enricher and worker
- Replace per-item create loop with single POST /user-products/batch call
  from RecognitionConfirmScreen
- Rebuild RecognitionConfirmScreen: amber qty border for low
  quantity_confidence, tappable product name → catalog picker,
  sort items by confidence, full L10n (no hardcoded strings)
- Add timestamps (HH:mm / d MMM HH:mm) to recent scan chips
- Show close-app hint on ProductJobWatchScreen (queued + processing)
- Refresh recentProductJobsProvider on watch screen init so new job
  appears without a manual pull-to-refresh
- App-level WidgetsBindingObserver refreshes product and dish job lists
  on resume, fixing stale lists after background/foreground transitions
- Add 9 new L10n keys across all 12 locales

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

client/lib/features/scan/recognition_service.dart

@@ -21,6 +21,7 @@ class RecognizedItem {
   String unit;
   final String category;
   final double confidence;
+  final double quantityConfidence;
   final String? primaryProductId;
   final int storageDays;
 
@@ -30,6 +31,7 @@ class RecognizedItem {
     required this.unit,
     required this.category,
     required this.confidence,
+    this.quantityConfidence = 1.0,
     this.primaryProductId,
     required this.storageDays,
   });
@@ -41,6 +43,7 @@ class RecognizedItem {
       unit: json['unit'] as String? ?? 'pcs',
       category: json['category'] as String? ?? 'other',
       confidence: (json['confidence'] as num?)?.toDouble() ?? 0.0,
+      quantityConfidence: (json['quantity_confidence'] as num?)?.toDouble() ?? 1.0,
       primaryProductId: json['mapping_id'] as String?,
       storageDays: json['storage_days'] as int? ?? 7,
     );