feat: add product selection step before meal planning

Inserts a new PlanProductsSheet as step 1 of the planning flow.
Users see their current products as a multi-select checklist (all
selected by default) before choosing the planning mode and dates.

- Empty state explains the benefit and offers "Add products" CTA
  while always allowing "Plan without products" to skip
- Selected product IDs flow through PlanMenuSheet →
  PlanDatePickerSheet → MenuService.generateForDates → backend
- Backend: added ProductIDs field to generate-menu request body;
  uses ListForPromptByIDs when set, ListForPrompt otherwise
- Backend: added Repository.ListForPromptByIDs (filtered SQL query)
- All 12 ARB locale files updated with planProducts* keys

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

client/lib/l10n/app_localizations_hi.dart

@@ -421,4 +421,36 @@ class AppLocalizationsHi extends AppLocalizations {
 
   @override
   String get planSuccess => 'मेनू की योजना बनाई गई!';
+
+  @override
+  String get planProductsTitle => 'मेनू के लिए उत्पाद';
+
+  @override
+  String get planProductsSubtitle =>
+      'AI रेसिपी बनाते समय चुने हुए उत्पादों को ध्यान में रखेगा';
+
+  @override
+  String get planProductsEmpty => 'कोई उत्पाद नहीं जोड़ा गया';
+
+  @override
+  String get planProductsEmptyMessage =>
+      'घर पर उपलब्ध उत्पाद जोड़ें — AI आपके पास पहले से मौजूद चीज़ों से रेसिपी सुझाएगा';
+
+  @override
+  String get planProductsAddProducts => 'उत्पाद जोड़ें';
+
+  @override
+  String get planProductsContinue => 'जारी रखें';
+
+  @override
+  String get planProductsSkip => 'उत्पाद चयन छोड़ें';
+
+  @override
+  String get planProductsSkipNoProducts => 'उत्पादों के बिना योजना बनाएं';
+
+  @override
+  String get planProductsSelectAll => 'सभी चुनें';
+
+  @override
+  String get planProductsDeselectAll => 'सभी हटाएं';
 }