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_es.arb

@@ -118,7 +118,9 @@
   "noResultsForQuery": "Nada encontrado para \"{query}\"",
   "@noResultsForQuery": {
     "placeholders": {
-      "query": { "type": "String" }
+      "query": {
+        "type": "String"
+      }
     }
   },
   "servingsLabel": "Porciones",
@@ -127,7 +129,9 @@
   "planningForDate": "",
   "@planningForDate": {
     "placeholders": {
-      "date": { "type": "String" }
+      "date": {
+        "type": "String"
+      }
     }
   },
   "markAsEaten": "Marcar como comido",
@@ -136,7 +140,6 @@
   "generateWeekSubtitle": "La IA creará un menú con desayuno, comida y cena para toda la semana",
   "generatingMenu": "Generando menú...",
   "dayPlannedLabel": "Día planificado",
-
   "planMenuButton": "Planificar comidas",
   "planMenuTitle": "¿Qué planificar?",
   "planOptionSingleMeal": "Una comida",
@@ -151,6 +154,16 @@
   "planSelectMealType": "Tipo de comida",
   "planSelectRange": "Seleccionar período",
   "planGenerateButton": "Planificar",
-  "planGenerating": "Generando plan\u2026",
-  "planSuccess": "¡Menú planificado!"
+  "planGenerating": "Generando plan…",
+  "planSuccess": "¡Menú planificado!",
+  "planProductsTitle": "Productos para el menú",
+  "planProductsSubtitle": "La IA tendrá en cuenta los productos seleccionados al generar recetas",
+  "planProductsEmpty": "No hay productos añadidos",
+  "planProductsEmptyMessage": "Añade productos que tengas en casa — la IA sugerirá recetas con lo que ya tienes",
+  "planProductsAddProducts": "Añadir productos",
+  "planProductsContinue": "Continuar",
+  "planProductsSkip": "Omitir selección de productos",
+  "planProductsSkipNoProducts": "Planificar sin productos",
+  "planProductsSelectAll": "Seleccionar todo",
+  "planProductsDeselectAll": "Deseleccionar todo"
 }