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/migrations/007_create_menu_plans.sql

@@ -0,0 +1,35 @@
+-- +goose Up
+
+CREATE TABLE menu_plans (
+    id         UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    user_id    UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    week_start DATE NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    UNIQUE(user_id, week_start)
+);
+
+CREATE TABLE menu_items (
+    id           UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    menu_plan_id UUID NOT NULL REFERENCES menu_plans(id) ON DELETE CASCADE,
+    day_of_week  INT  NOT NULL CHECK (day_of_week BETWEEN 1 AND 7),
+    meal_type    TEXT NOT NULL CHECK (meal_type IN ('breakfast','lunch','dinner')),
+    recipe_id    UUID REFERENCES saved_recipes(id) ON DELETE SET NULL,
+    recipe_data  JSONB,
+    UNIQUE(menu_plan_id, day_of_week, meal_type)
+);
+
+-- Stores the generated shopping list for a menu plan.
+-- items is a JSONB array of {name, category, amount, unit, checked, in_stock}.
+CREATE TABLE shopping_lists (
+    id           UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    user_id      UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    menu_plan_id UUID REFERENCES menu_plans(id) ON DELETE CASCADE,
+    items        JSONB NOT NULL DEFAULT '[]',
+    generated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    UNIQUE(user_id, menu_plan_id)
+);
+
+-- +goose Down
+DROP TABLE shopping_lists;
+DROP TABLE menu_items;
+DROP TABLE menu_plans;