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>

backend/internal/adapters/ai/types.go

@@ -94,16 +94,20 @@ type ReceiptResult struct {
 	Unrecognized []UnrecognizedItem `json:"unrecognized"`
 }
 
-// DishResult is the result of dish recognition.
+// DishCandidate is a single dish recognition candidate with estimated nutrition.
+type DishCandidate struct {
+	DishName    string  `json:"dish_name"`
+	WeightGrams int     `json:"weight_grams"`
+	Calories    float64 `json:"calories"`
+	ProteinG    float64 `json:"protein_g"`
+	FatG        float64 `json:"fat_g"`
+	CarbsG      float64 `json:"carbs_g"`
+	Confidence  float64 `json:"confidence"`
+}
+
+// DishResult is the result of dish recognition with multiple ranked candidates.
 type DishResult struct {
-	DishName      string   `json:"dish_name"`
-	WeightGrams   int      `json:"weight_grams"`
-	Calories      float64  `json:"calories"`
-	ProteinG      float64  `json:"protein_g"`
-	FatG          float64  `json:"fat_g"`
-	CarbsG        float64  `json:"carbs_g"`
-	Confidence    float64  `json:"confidence"`
-	SimilarDishes []string `json:"similar_dishes"`
+	Candidates []DishCandidate `json:"candidates"`
 }
 
 // IngredientTranslation holds the localized name and aliases for one language.