feat: implement Iteration 3 — product/receipt/dish recognition

Backend:
- gemini/client.go: refactor to shared callGroq transport; add
  generateVisionContent using llama-3.2-11b-vision-preview model
- gemini/recognition.go: RecognizeReceipt, RecognizeProducts,
  RecognizeDish (vision), ClassifyIngredient (text); shared parseJSON helper
- ingredient/repository.go: add FuzzyMatch (wraps Search, returns best hit)
- recognition/handler.go: POST /ai/recognize-receipt, /ai/recognize-products,
  /ai/recognize-dish; enrichItems with fuzzy match + AI classify fallback;
  parallel multi-image processing with deduplication
- server.go + main.go: wire recognition handler under /ai routes

Flutter:
- pubspec.yaml: add image_picker ^1.1.0
- AndroidManifest.xml: add CAMERA and READ_EXTERNAL_STORAGE permissions
- Info.plist: add NSCameraUsageDescription and NSPhotoLibraryUsageDescription
- recognition_service.dart: RecognitionService wrapping /ai/* endpoints;
  RecognizedItem, ReceiptResult, DishResult models
- scan_screen.dart: mode selector (receipt / products / dish / manual);
  image source picker; loading overlay; navigates to confirm or dish screen
- recognition_confirm_screen.dart: editable list of recognized items;
  inline qty/unit editing; swipe-to-delete; batch-add to pantry
- dish_result_screen.dart: dish name, KBZHU breakdown, similar dishes chips
- app_router.dart: /scan, /scan/confirm, /scan/dish routes (no bottom nav)
- products_screen.dart: FAB now shows bottom sheet with Manual / Scan options

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

client/lib/features/scan/recognition_service.dart

@@ -0,0 +1,150 @@
+import 'dart:convert';
+import 'dart:io';
+
+import '../../core/api/api_client.dart';
+
+// ---------------------------------------------------------------------------
+// Models
+// ---------------------------------------------------------------------------
+
+class RecognizedItem {
+  final String name;
+  double quantity;
+  String unit;
+  final String category;
+  final double confidence;
+  final String? mappingId;
+  final int storageDays;
+
+  RecognizedItem({
+    required this.name,
+    required this.quantity,
+    required this.unit,
+    required this.category,
+    required this.confidence,
+    this.mappingId,
+    required this.storageDays,
+  });
+
+  factory RecognizedItem.fromJson(Map<String, dynamic> json) {
+    return RecognizedItem(
+      name: json['name'] as String? ?? '',
+      quantity: (json['quantity'] as num?)?.toDouble() ?? 1.0,
+      unit: json['unit'] as String? ?? 'шт',
+      category: json['category'] as String? ?? 'other',
+      confidence: (json['confidence'] as num?)?.toDouble() ?? 0.0,
+      mappingId: json['mapping_id'] as String?,
+      storageDays: json['storage_days'] as int? ?? 7,
+    );
+  }
+}
+
+class UnrecognizedItem {
+  final String rawText;
+  final double? price;
+
+  const UnrecognizedItem({required this.rawText, this.price});
+
+  factory UnrecognizedItem.fromJson(Map<String, dynamic> json) {
+    return UnrecognizedItem(
+      rawText: json['raw_text'] as String? ?? '',
+      price: (json['price'] as num?)?.toDouble(),
+    );
+  }
+}
+
+class ReceiptResult {
+  final List<RecognizedItem> items;
+  final List<UnrecognizedItem> unrecognized;
+
+  const ReceiptResult({required this.items, required this.unrecognized});
+}
+
+class DishResult {
+  final String dishName;
+  final int weightGrams;
+  final double calories;
+  final double proteinG;
+  final double fatG;
+  final double carbsG;
+  final double confidence;
+  final List<String> similarDishes;
+
+  const DishResult({
+    required this.dishName,
+    required this.weightGrams,
+    required this.calories,
+    required this.proteinG,
+    required this.fatG,
+    required this.carbsG,
+    required this.confidence,
+    required this.similarDishes,
+  });
+
+  factory DishResult.fromJson(Map<String, dynamic> json) {
+    return DishResult(
+      dishName: json['dish_name'] as String? ?? '',
+      weightGrams: json['weight_grams'] as int? ?? 0,
+      calories: (json['calories'] as num?)?.toDouble() ?? 0,
+      proteinG: (json['protein_g'] as num?)?.toDouble() ?? 0,
+      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() ??
+          [],
+    );
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Service
+// ---------------------------------------------------------------------------
+
+class RecognitionService {
+  const RecognitionService(this._client);
+
+  final ApiClient _client;
+
+  /// Recognizes food items from a receipt photo.
+  Future<ReceiptResult> recognizeReceipt(File image) async {
+    final payload = await _buildImagePayload(image);
+    final data = await _client.post('/ai/recognize-receipt', data: payload);
+    return ReceiptResult(
+      items: (data['items'] as List<dynamic>? ?? [])
+          .map((e) => RecognizedItem.fromJson(e as Map<String, dynamic>))
+          .toList(),
+      unrecognized: (data['unrecognized'] as List<dynamic>? ?? [])
+          .map((e) => UnrecognizedItem.fromJson(e as Map<String, dynamic>))
+          .toList(),
+    );
+  }
+
+  /// Recognizes food items from 1–3 product photos.
+  Future<List<RecognizedItem>> recognizeProducts(List<File> images) async {
+    final imageList = await Future.wait(images.map(_buildImagePayload));
+    final data = await _client.post(
+      '/ai/recognize-products',
+      data: {'images': imageList},
+    );
+    return (data['items'] as List<dynamic>? ?? [])
+        .map((e) => RecognizedItem.fromJson(e as Map<String, dynamic>))
+        .toList();
+  }
+
+  /// Recognizes a dish and estimates its nutritional content.
+  Future<DishResult> recognizeDish(File image) async {
+    final payload = await _buildImagePayload(image);
+    final data = await _client.post('/ai/recognize-dish', data: payload);
+    return DishResult.fromJson(data);
+  }
+
+  Future<Map<String, String>> _buildImagePayload(File image) async {
+    final bytes = await image.readAsBytes();
+    final base64Data = base64Encode(bytes);
+    final ext = image.path.split('.').last.toLowerCase();
+    final mimeType = ext == 'png' ? 'image/png' : 'image/jpeg';
+    return {'image_base64': base64Data, 'mime_type': mimeType};
+  }
+}