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_ko.dart

@@ -418,4 +418,35 @@ class AppLocalizationsKo extends AppLocalizations {
 
   @override
   String get planSuccess => '메뉴가 계획되었습니다!';
+
+  @override
+  String get planProductsTitle => '메뉴 재료';
+
+  @override
+  String get planProductsSubtitle => 'AI가 레시피 생성 시 선택한 재료를 고려합니다';
+
+  @override
+  String get planProductsEmpty => '추가된 재료가 없습니다';
+
+  @override
+  String get planProductsEmptyMessage =>
+      '집에 있는 재료를 추가하세요 — AI가 이미 있는 재료로 레시피를 제안합니다';
+
+  @override
+  String get planProductsAddProducts => '재료 추가';
+
+  @override
+  String get planProductsContinue => '계속';
+
+  @override
+  String get planProductsSkip => '재료 선택 건너뛰기';
+
+  @override
+  String get planProductsSkipNoProducts => '재료 없이 계획하기';
+
+  @override
+  String get planProductsSelectAll => '모두 선택';
+
+  @override
+  String get planProductsDeselectAll => '모두 해제';
 }