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/diary/model.go

@@ -0,0 +1,33 @@
+package diary
+
+import "time"
+
+// Entry is a single meal diary record.
+type Entry struct {
+	ID        string    `json:"id"`
+	Date      string    `json:"date"` // YYYY-MM-DD
+	MealType  string    `json:"meal_type"`
+	Name      string    `json:"name"`
+	Portions  float64   `json:"portions"`
+	Calories  *float64  `json:"calories,omitempty"`
+	ProteinG  *float64  `json:"protein_g,omitempty"`
+	FatG      *float64  `json:"fat_g,omitempty"`
+	CarbsG    *float64  `json:"carbs_g,omitempty"`
+	Source    string    `json:"source"`
+	RecipeID  *string   `json:"recipe_id,omitempty"`
+	CreatedAt time.Time `json:"created_at"`
+}
+
+// CreateRequest is the body for POST /diary.
+type CreateRequest struct {
+	Date     string  `json:"date"`
+	MealType string  `json:"meal_type"`
+	Name     string  `json:"name"`
+	Portions float64 `json:"portions"`
+	Calories *float64 `json:"calories"`
+	ProteinG *float64 `json:"protein_g"`
+	FatG     *float64 `json:"fat_g"`
+	CarbsG   *float64 `json:"carbs_g"`
+	Source   string  `json:"source"`
+	RecipeID *string `json:"recipe_id"`
+}