feat: meal tracking, dish recognition UX improvements, English AI prompts

Backend:
- Translate all recognition prompts (receipt, products, dish) from Russian to English
- Add lang parameter to Recognizer interface and pass locale.FromContext in handlers
- DishResult type uses candidates array for multi-candidate responses

Client:
- Add meal tracking: diary provider, date selector, meal type model
- DishResult parser: backward-compatible with legacy flat format and new candidates format
- DishResultScreen: sticky bottom button, full-width portion/meal-type inputs,
  КБЖУ disclaimer moved under nutrition card, add date field to diary POST body
- Recognition prompts now return dish/product names in user's preferred language
- Onboarding, profile, home screen visual updates

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

client/lib/shared/models/meal_type.dart

@@ -0,0 +1,29 @@
+/// A configurable meal type that the user tracks throughout the day.
+class MealTypeOption {
+  final String id;
+  final String label;
+  final String emoji;
+
+  const MealTypeOption({
+    required this.id,
+    required this.label,
+    required this.emoji,
+  });
+}
+
+/// All meal types available for selection.
+const kAllMealTypes = [
+  MealTypeOption(id: 'breakfast',       label: 'Завтрак',        emoji: '🌅'),
+  MealTypeOption(id: 'second_breakfast', label: 'Второй завтрак', emoji: '☕'),
+  MealTypeOption(id: 'lunch',           label: 'Обед',           emoji: '🍽️'),
+  MealTypeOption(id: 'afternoon_snack', label: 'Полдник',        emoji: '🥗'),
+  MealTypeOption(id: 'dinner',          label: 'Ужин',           emoji: '🌙'),
+  MealTypeOption(id: 'snack',           label: 'Перекус',        emoji: '🍎'),
+];
+
+/// Default meal type IDs assigned to new users.
+const kDefaultMealTypeIds = ['breakfast', 'lunch', 'dinner'];
+
+/// Returns the [MealTypeOption] for the given [id], or null if not found.
+MealTypeOption? mealTypeById(String id) =>
+    kAllMealTypes.where((option) => option.id == id).firstOrNull;

client/lib/shared/models/user.dart

@@ -1,5 +1,7 @@
 import 'package:json_annotation/json_annotation.dart';
 
+import 'meal_type.dart';
+
 part 'user.g.dart';
 
 @JsonSerializable()
@@ -59,4 +61,12 @@ class User {
   bool get hasCompletedOnboarding =>
       heightCm != null && weightKg != null && dateOfBirth != null &&
       gender != null && goal != null && activity != null;
+
+  /// Returns the user's configured meal type IDs from preferences,
+  /// falling back to the default set if not yet configured.
+  List<String> get mealTypes {
+    final value = preferences['meal_types'];
+    if (value is List && value.isNotEmpty) return List<String>.from(value);
+    return List<String>.from(kDefaultMealTypeIds);
+  }
 }