feat: dish recognition UX, background mode, and backend bug fixes

Flutter client:
- Progress dialog: redesigned with pulsing animated icon, info hint about
  background mode, full-width Minimize button; dismiss signal via ValueNotifier
  so the dialog always closes regardless of widget lifecycle
- Background recognition: when user taps Minimize, wasMinimizedByUser flag is
  set; on completion a snackbar is shown instead of opening DishResultSheet
  directly; snackbar action opens the sheet on demand
- Fix dialog spinning forever: finally block guarantees dismissSignal=true on
  all exit paths including early returns from context.mounted checks
- Fix DishResultSheet not appearing: add ValueKey to _DailyMealsSection and
  meal card Padding so Flutter reuses elements when _TodayJobsWidget is
  inserted/removed from the SliverChildListDelegate list
- todayJobsProvider refresh: added refresh() method; called after job submit
  and on DishJobDone; all ref.read() calls guarded with context.mounted checks
- food_search_sheet: scan buttons replaced with full-width stacked OutlinedButtons
- app.dart: WidgetsBindingObserver refreshes scan providers on app resume
- L10n: added dishRecognitionHint and minimize keys to all 12 locales

Backend:
- migrations/003: ALTER TYPE recipe_source ADD VALUE 'recommendation' to fix
  22P02 error in GET /home/summary -> getRecommendations()
- item_enricher: normalizeProductCategory() validates AI-returned category
  against known slugs, falls back to "other" — fixes products_category_fkey
  FK violation during receipt recognition
- recognition prompt: enumerate valid categories so AI returns correct values

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

client/lib/l10n/app_localizations_de.dart

@@ -579,4 +579,11 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get scanJobCloseHint =>
       'Du kannst die App schließen — dieser Scan erscheint in Letzte Scans auf dem Produktbildschirm';
+
+  @override
+  String get minimize => 'Minimieren';
+
+  @override
+  String get dishRecognitionHint =>
+      'Du kannst minimieren — das Ergebnis erscheint auf dem Startbildschirm, wenn fertig';
 }