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_zh.arb

@@ -118,7 +118,9 @@
   "noResultsForQuery": "未找到 \"{query}\" 的结果",
   "@noResultsForQuery": {
     "placeholders": {
-      "query": { "type": "String" }
+      "query": {
+        "type": "String"
+      }
     }
   },
   "servingsLabel": "份数",
@@ -127,7 +129,9 @@
   "planningForDate": "",
   "@planningForDate": {
     "placeholders": {
-      "date": { "type": "String" }
+      "date": {
+        "type": "String"
+      }
     }
   },
   "markAsEaten": "标记为已吃",
@@ -136,7 +140,6 @@
   "generateWeekSubtitle": "AI将为整周创建含早餐、午餐和晚餐的菜单",
   "generatingMenu": "正在生成菜单...",
   "dayPlannedLabel": "今日已规划",
-
   "planMenuButton": "规划餐食",
   "planMenuTitle": "规划什么？",
   "planOptionSingleMeal": "单次餐食",
@@ -151,6 +154,16 @@
   "planSelectMealType": "餐食类型",
   "planSelectRange": "选择时间段",
   "planGenerateButton": "规划",
-  "planGenerating": "正在生成计划\u2026",
-  "planSuccess": "菜单已规划！"
+  "planGenerating": "正在生成计划…",
+  "planSuccess": "菜单已规划！",
+  "planProductsTitle": "菜单食材",
+  "planProductsSubtitle": "AI在生成食谱时会考虑所选食材",
+  "planProductsEmpty": "尚未添加食材",
+  "planProductsEmptyMessage": "添加您家中的食材 — AI将根据您已有的食材推荐食谱",
+  "planProductsAddProducts": "添加食材",
+  "planProductsContinue": "继续",
+  "planProductsSkip": "跳过食材选择",
+  "planProductsSkipNoProducts": "不选食材直接规划",
+  "planProductsSelectAll": "全选",
+  "planProductsDeselectAll": "取消全选"
 }