feat: flexible meal planning wizard — plan 1 meal, 1 day, several days, or a week

Backend:
- migration 005: expand menu_items.meal_type CHECK to all 6 types (second_breakfast, afternoon_snack, snack)
- ai/types.go: add Days and MealTypes to MenuRequest for partial generation
- openai/menu.go: parametrize GenerateMenu — use requested meal types and day count; add caloric fractions for all 6 meal types
- menu/repository.go: add UpsertItemsInTx for partial upsert (preserves existing slots); fix meal_type sort order in GetByWeek
- menu/handler.go: add dates+meal_types path to POST /ai/generate-menu; extract fetchImages/saveRecipes helpers; returns {"plans":[...]} for dates mode; backward-compatible with week mode

Client:
- PlanMenuSheet: bottom sheet with 4 planning horizon options
- PlanDatePickerSheet: adaptive sheet with date strip (single day/meal) or custom CalendarRangePicker (multi-day/week); sliding 7-day window for week mode
- menu_service.dart: add generateForDates
- menu_provider.dart: add PlanMenuService (generates + invalidates week providers), lastPlannedDateProvider
- home_screen.dart: add _PlanMenuButton card below quick actions; opens planning wizard
- l10n: 16 new keys for planning UI across all 12 languages

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

client/lib/l10n/app_localizations.dart

@@ -831,6 +831,102 @@ abstract class AppLocalizations {
   /// In en, this message translates to:
   /// **'Week planned'**
   String get weekPlannedLabel;
+
+  /// No description provided for @planMenuButton.
+  ///
+  /// In en, this message translates to:
+  /// **'Plan meals'**
+  String get planMenuButton;
+
+  /// No description provided for @planMenuTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'What to plan?'**
+  String get planMenuTitle;
+
+  /// No description provided for @planOptionSingleMeal.
+  ///
+  /// In en, this message translates to:
+  /// **'Single meal'**
+  String get planOptionSingleMeal;
+
+  /// No description provided for @planOptionSingleMealDesc.
+  ///
+  /// In en, this message translates to:
+  /// **'Choose a day and meal type'**
+  String get planOptionSingleMealDesc;
+
+  /// No description provided for @planOptionDay.
+  ///
+  /// In en, this message translates to:
+  /// **'One day'**
+  String get planOptionDay;
+
+  /// No description provided for @planOptionDayDesc.
+  ///
+  /// In en, this message translates to:
+  /// **'All meals for one day'**
+  String get planOptionDayDesc;
+
+  /// No description provided for @planOptionDays.
+  ///
+  /// In en, this message translates to:
+  /// **'Several days'**
+  String get planOptionDays;
+
+  /// No description provided for @planOptionDaysDesc.
+  ///
+  /// In en, this message translates to:
+  /// **'Custom date range'**
+  String get planOptionDaysDesc;
+
+  /// No description provided for @planOptionWeek.
+  ///
+  /// In en, this message translates to:
+  /// **'A week'**
+  String get planOptionWeek;
+
+  /// No description provided for @planOptionWeekDesc.
+  ///
+  /// In en, this message translates to:
+  /// **'7 days at once'**
+  String get planOptionWeekDesc;
+
+  /// No description provided for @planSelectDate.
+  ///
+  /// In en, this message translates to:
+  /// **'Select date'**
+  String get planSelectDate;
+
+  /// No description provided for @planSelectMealType.
+  ///
+  /// In en, this message translates to:
+  /// **'Meal type'**
+  String get planSelectMealType;
+
+  /// No description provided for @planSelectRange.
+  ///
+  /// In en, this message translates to:
+  /// **'Select period'**
+  String get planSelectRange;
+
+  /// No description provided for @planGenerateButton.
+  ///
+  /// In en, this message translates to:
+  /// **'Plan'**
+  String get planGenerateButton;
+
+  /// No description provided for @planGenerating.
+  ///
+  /// In en, this message translates to:
+  /// **'Generating plan…'**
+  String get planGenerating;
+
+  /// No description provided for @planSuccess.
+  ///
+  /// In en, this message translates to:
+  /// **'Menu planned!'**
+  String get planSuccess;
 }
 
 class _AppLocalizationsDelegate