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/features/scan/recognition_service.dart

@@ -61,7 +61,8 @@ class ReceiptResult {
   const ReceiptResult({required this.items, required this.unrecognized});
 }
 
-class DishResult {
+/// A single dish recognition candidate with estimated nutrition for the portion in the photo.
+class DishCandidate {
   final String dishName;
   final int weightGrams;
   final double calories;
@@ -69,9 +70,8 @@ class DishResult {
   final double fatG;
   final double carbsG;
   final double confidence;
-  final List<String> similarDishes;
 
-  const DishResult({
+  const DishCandidate({
     required this.dishName,
     required this.weightGrams,
     required this.calories,
@@ -79,11 +79,10 @@ class DishResult {
     required this.fatG,
     required this.carbsG,
     required this.confidence,
-    required this.similarDishes,
   });
 
-  factory DishResult.fromJson(Map<String, dynamic> json) {
-    return DishResult(
+  factory DishCandidate.fromJson(Map<String, dynamic> json) {
+    return DishCandidate(
       dishName: json['dish_name'] as String? ?? '',
       weightGrams: json['weight_grams'] as int? ?? 0,
       calories: (json['calories'] as num?)?.toDouble() ?? 0,
@@ -91,14 +90,46 @@ class DishResult {
       fatG: (json['fat_g'] as num?)?.toDouble() ?? 0,
       carbsG: (json['carbs_g'] as num?)?.toDouble() ?? 0,
       confidence: (json['confidence'] as num?)?.toDouble() ?? 0,
-      similarDishes: (json['similar_dishes'] as List<dynamic>?)
-              ?.map((e) => e as String)
-              .toList() ??
-          [],
     );
   }
 }
 
+/// Result of dish recognition: ordered list of candidates (best match first).
+class DishResult {
+  final List<DishCandidate> candidates;
+
+  const DishResult({required this.candidates});
+
+  /// The best matching candidate.
+  DishCandidate get best => candidates.first;
+
+  // Convenience getters delegating to the best candidate.
+  String get dishName    => best.dishName;
+  int    get weightGrams => best.weightGrams;
+  double get calories    => best.calories;
+  double get proteinG    => best.proteinG;
+  double get fatG        => best.fatG;
+  double get carbsG      => best.carbsG;
+  double get confidence  => best.confidence;
+
+  factory DishResult.fromJson(Map<String, dynamic> json) {
+    // New format: {"candidates": [...]}
+    if (json['candidates'] is List) {
+      final candidatesList = (json['candidates'] as List<dynamic>)
+          .map((element) => DishCandidate.fromJson(element as Map<String, dynamic>))
+          .toList();
+      return DishResult(candidates: candidatesList);
+    }
+
+    // Legacy flat format: {"dish_name": "...", "calories": ..., ...}
+    if (json['dish_name'] != null) {
+      return DishResult(candidates: [DishCandidate.fromJson(json)]);
+    }
+
+    return const DishResult(candidates: []);
+  }
+}
+
 // ---------------------------------------------------------------------------
 // Service
 // ---------------------------------------------------------------------------