feat: implement Iteration 4 — menu planning, shopping list, diary

Backend:
- Migrations 007 (menu_plans, menu_items, shopping_lists) and
  008 (meal_diary)
- gemini/menu.go: GenerateMenu — 7-day × 3-meal plan via one Groq call
- internal/menu: model, repository (GetByWeek, SaveMenuInTx,
  shopping list CRUD), handler (GET/PUT/DELETE /menu,
  POST /ai/generate-menu, shopping list endpoints)
- internal/diary: model, repository, handler (GET/POST/DELETE /diary)
- Increase server WriteTimeout to 120s for long AI calls
- api_client.go: add patch() and postList() helpers

Flutter:
- shared/models: menu.dart, shopping_item.dart, diary_entry.dart
- features/menu: menu_service.dart, menu_provider.dart
  (MenuNotifier, ShoppingListNotifier, DiaryNotifier with family)
- MenuScreen: 7-day view, week nav, skeleton on generation,
  generate FAB with confirmation dialog
- ShoppingListScreen: items by category, optimistic checkbox toggle
- DiaryScreen: daily entries with swipe-to-delete, add-entry sheet
- Router: /menu/shopping-list and /menu/diary routes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/menu/model.go

@@ -0,0 +1,56 @@
+package menu
+
+// MenuPlan is a weekly meal plan for a user.
+type MenuPlan struct {
+	ID        string    `json:"id"`
+	WeekStart string    `json:"week_start"` // YYYY-MM-DD (Monday)
+	Days      []MenuDay `json:"days"`
+}
+
+// MenuDay groups three meal slots for one calendar day.
+type MenuDay struct {
+	Day           int        `json:"day"` // 1=Monday … 7=Sunday
+	Date          string     `json:"date"`
+	Meals         []MealSlot `json:"meals"`
+	TotalCalories float64    `json:"total_calories"`
+}
+
+// MealSlot holds a single meal within a day.
+type MealSlot struct {
+	ID       string      `json:"id"`
+	MealType string      `json:"meal_type"` // breakfast | lunch | dinner
+	Recipe   *MenuRecipe `json:"recipe,omitempty"`
+}
+
+// MenuRecipe is a thin projection of a saved recipe used in the menu view.
+type MenuRecipe struct {
+	ID        string        `json:"id"`
+	Title     string        `json:"title"`
+	ImageURL  string        `json:"image_url"`
+	Nutrition NutritionInfo `json:"nutrition_per_serving"`
+}
+
+// NutritionInfo holds macronutrient data.
+type NutritionInfo struct {
+	Calories float64 `json:"calories"`
+	ProteinG float64 `json:"protein_g"`
+	FatG     float64 `json:"fat_g"`
+	CarbsG   float64 `json:"carbs_g"`
+}
+
+// PlanItem is the input needed to create one menu_items row.
+type PlanItem struct {
+	DayOfWeek int
+	MealType  string
+	RecipeID  string
+}
+
+// ShoppingItem is one entry in the shopping list.
+type ShoppingItem struct {
+	Name     string  `json:"name"`
+	Category string  `json:"category"`
+	Amount   float64 `json:"amount"`
+	Unit     string  `json:"unit"`
+	Checked  bool    `json:"checked"`
+	InStock  float64 `json:"in_stock"`
+}