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/repository.go

@@ -0,0 +1,104 @@
+package diary
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// ErrNotFound is returned when a diary entry does not exist for the user.
+var ErrNotFound = errors.New("diary entry not found")
+
+// Repository handles persistence for meal diary entries.
+type Repository struct {
+	pool *pgxpool.Pool
+}
+
+// NewRepository creates a new Repository.
+func NewRepository(pool *pgxpool.Pool) *Repository {
+	return &Repository{pool: pool}
+}
+
+// ListByDate returns all diary entries for a user on a given date (YYYY-MM-DD).
+func (r *Repository) ListByDate(ctx context.Context, userID, date string) ([]*Entry, error) {
+	rows, err := r.pool.Query(ctx, `
+		SELECT id, date::text, meal_type, name, portions,
+		       calories, protein_g, fat_g, carbs_g,
+		       source, recipe_id, created_at
+		FROM meal_diary
+		WHERE user_id = $1 AND date = $2::date
+		ORDER BY created_at ASC`, userID, date)
+	if err != nil {
+		return nil, fmt.Errorf("list diary: %w", err)
+	}
+	defer rows.Close()
+
+	var result []*Entry
+	for rows.Next() {
+		e, err := scanEntry(rows)
+		if err != nil {
+			return nil, fmt.Errorf("scan diary entry: %w", err)
+		}
+		result = append(result, e)
+	}
+	return result, rows.Err()
+}
+
+// Create inserts a new diary entry and returns the stored record.
+func (r *Repository) Create(ctx context.Context, userID string, req CreateRequest) (*Entry, error) {
+	portions := req.Portions
+	if portions <= 0 {
+		portions = 1
+	}
+	source := req.Source
+	if source == "" {
+		source = "manual"
+	}
+
+	row := r.pool.QueryRow(ctx, `
+		INSERT INTO meal_diary (user_id, date, meal_type, name, portions,
+		    calories, protein_g, fat_g, carbs_g, source, recipe_id)
+		VALUES ($1, $2::date, $3, $4, $5, $6, $7, $8, $9, $10, $11)
+		RETURNING id, date::text, meal_type, name, portions,
+		    calories, protein_g, fat_g, carbs_g, source, recipe_id, created_at`,
+		userID, req.Date, req.MealType, req.Name, portions,
+		req.Calories, req.ProteinG, req.FatG, req.CarbsG,
+		source, req.RecipeID,
+	)
+	return scanEntry(row)
+}
+
+// Delete removes a diary entry for the given user.
+func (r *Repository) Delete(ctx context.Context, id, userID string) error {
+	tag, err := r.pool.Exec(ctx,
+		`DELETE FROM meal_diary WHERE id = $1 AND user_id = $2`, id, userID)
+	if err != nil {
+		return fmt.Errorf("delete diary entry: %w", err)
+	}
+	if tag.RowsAffected() == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
+// --- helpers ---
+
+type scannable interface {
+	Scan(dest ...any) error
+}
+
+func scanEntry(s scannable) (*Entry, error) {
+	var e Entry
+	err := s.Scan(
+		&e.ID, &e.Date, &e.MealType, &e.Name, &e.Portions,
+		&e.Calories, &e.ProteinG, &e.FatG, &e.CarbsG,
+		&e.Source, &e.RecipeID, &e.CreatedAt,
+	)
+	if errors.Is(err, pgx.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	return &e, err
+}