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>

backend/internal/domain/recognition/item_enricher.go

@@ -26,12 +26,13 @@ func (enricher *itemEnricher) enrich(enrichContext context.Context, items []ai.R
 	result := make([]EnrichedItem, 0, len(items))
 	for _, item := range items {
 		enriched := EnrichedItem{
-			Name:        item.Name,
-			Quantity:    item.Quantity,
-			Unit:        item.Unit,
-			Category:    item.Category,
-			Confidence:  item.Confidence,
-			StorageDays: 7, // sensible default
+			Name:               item.Name,
+			Quantity:           item.Quantity,
+			Unit:               item.Unit,
+			Category:           item.Category,
+			Confidence:         item.Confidence,
+			QuantityConfidence: item.QuantityConfidence,
+			StorageDays:        7, // sensible default
 		}
 
 		catalogProduct, matchError := enricher.productRepo.FuzzyMatch(enrichContext, item.Name)