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/features/home/home_screen.dart

@@ -19,6 +19,7 @@ import '../diary/food_search_sheet.dart';
 import '../menu/menu_provider.dart';
 import '../menu/plan_date_picker_sheet.dart';
 import '../menu/plan_menu_sheet.dart';
+import '../menu/plan_products_sheet.dart';
 import '../profile/profile_provider.dart';
 import '../scan/dish_result_screen.dart';
 import '../scan/recognition_service.dart';
@@ -1597,19 +1598,33 @@ class _FutureDayPlanButton extends ConsumerWidget {
 
   void _openPlanSheet(BuildContext context, WidgetRef ref) {
     final defaultStart = DateTime.parse(dateString);
+    // Step 1: product selection
     showModalBottomSheet<void>(
       context: context,
       isScrollControlled: true,
       useSafeArea: true,
-      builder: (_) => PlanMenuSheet(
-        onModeSelected: (mode) {
+      builder: (_) => PlanProductsSheet(
+        onContinue: (selectedProductIds) {
+          // Step 2: planning mode selection
           showModalBottomSheet<void>(
             context: context,
             isScrollControlled: true,
             useSafeArea: true,
-            builder: (_) => PlanDatePickerSheet(
-              mode: mode,
-              defaultStart: defaultStart,
+            builder: (_) => PlanMenuSheet(
+              selectedProductIds: selectedProductIds,
+              onModeSelected: (mode, productIds) {
+                // Step 3: date / meal type selection
+                showModalBottomSheet<void>(
+                  context: context,
+                  isScrollControlled: true,
+                  useSafeArea: true,
+                  builder: (_) => PlanDatePickerSheet(
+                    mode: mode,
+                    defaultStart: defaultStart,
+                    selectedProductIds: productIds,
+                  ),
+                );
+              },
             ),
           );
         },