feat: implement Iteration 1 — AI recipe recommendations

Backend:
- Add Groq LLM client (llama-3.3-70b) for recipe generation with JSON
  retry strategy (retries only on parse errors, not API errors)
- Add Pexels client for parallel photo search per recipe
- Add saved_recipes table (migration 004) with JSONB fields
- Add GET /recommendations endpoint (profile-aware prompt building)
- Add POST/GET/GET{id}/DELETE /saved-recipes CRUD endpoints
- Wire gemini, pexels, recommendation, savedrecipe packages in main.go

Flutter:
- Add Recipe, SavedRecipe models with json_serializable
- Add RecipeService (getRecommendations, getSavedRecipes, save, delete)
- Add RecommendationsNotifier and SavedRecipesNotifier (Riverpod)
- Add RecommendationsScreen with skeleton loading and refresh FAB
- Add RecipeDetailScreen (SliverAppBar, nutrition tooltip, steps with timer)
- Add SavedRecipesScreen with Dismissible swipe-to-delete and empty state
- Update RecipesScreen to TabBar (Recommendations / Saved)
- Add /recipe-detail route outside ShellRoute (no bottom nav)
- Extend ApiClient with getList() and deleteVoid()

Project:
- Add CLAUDE.md with English-only rule for comments and commit messages

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

backend/internal/ingredient/model.go

@@ -0,0 +1,28 @@
+package ingredient
+
+import (
+	"encoding/json"
+	"time"
+)
+
+// IngredientMapping is the canonical ingredient record used to link
+// user products, recipe ingredients, and Spoonacular data.
+type IngredientMapping struct {
+	ID              string          `json:"id"`
+	CanonicalName   string          `json:"canonical_name"`
+	CanonicalNameRu *string         `json:"canonical_name_ru"`
+	SpoonacularID   *int            `json:"spoonacular_id"`
+	Aliases         json.RawMessage `json:"aliases"`    // []string
+	Category        *string         `json:"category"`
+	DefaultUnit     *string         `json:"default_unit"`
+
+	CaloriesPer100g *float64 `json:"calories_per_100g"`
+	ProteinPer100g  *float64 `json:"protein_per_100g"`
+	FatPer100g      *float64 `json:"fat_per_100g"`
+	CarbsPer100g    *float64 `json:"carbs_per_100g"`
+	FiberPer100g    *float64 `json:"fiber_per_100g"`
+
+	StorageDays *int      `json:"storage_days"`
+	CreatedAt   time.Time `json:"created_at"`
+	UpdatedAt   time.Time `json:"updated_at"`
+}