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_ja.arb

@@ -118,7 +118,9 @@
   "noResultsForQuery": "「{query}」の検索結果はありません",
   "@noResultsForQuery": {
     "placeholders": {
-      "query": { "type": "String" }
+      "query": {
+        "type": "String"
+      }
     }
   },
   "servingsLabel": "人前",
@@ -127,7 +129,9 @@
   "planningForDate": "",
   "@planningForDate": {
     "placeholders": {
-      "date": { "type": "String" }
+      "date": {
+        "type": "String"
+      }
     }
   },
   "markAsEaten": "食べた印をつける",
@@ -136,7 +140,6 @@
   "generateWeekSubtitle": "AIが一週間の朝食・昼食・夕食のメニューを作成します",
   "generatingMenu": "メニューを生成中...",
   "dayPlannedLabel": "日の計画済み",
-
   "planMenuButton": "食事を計画する",
   "planMenuTitle": "何を計画する？",
   "planOptionSingleMeal": "1食",
@@ -151,6 +154,16 @@
   "planSelectMealType": "食事タイプ",
   "planSelectRange": "期間を選択",
   "planGenerateButton": "計画する",
-  "planGenerating": "プランを生成中\u2026",
-  "planSuccess": "メニューが計画されました！"
+  "planGenerating": "プランを生成中…",
+  "planSuccess": "メニューが計画されました！",
+  "planProductsTitle": "メニューの食材",
+  "planProductsSubtitle": "AIはレシピ生成時に選択した食材を考慮します",
+  "planProductsEmpty": "食材が追加されていません",
+  "planProductsEmptyMessage": "家にある食材を追加してください — AIが手持ちの食材でレシピを提案します",
+  "planProductsAddProducts": "食材を追加",
+  "planProductsContinue": "続ける",
+  "planProductsSkip": "食材選択をスキップ",
+  "planProductsSkipNoProducts": "食材なしでプランニング",
+  "planProductsSelectAll": "すべて選択",
+  "planProductsDeselectAll": "すべて解除"
 }