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/migrations/004_create_saved_recipes.sql

@@ -0,0 +1,25 @@
+-- +goose Up
+CREATE TABLE saved_recipes (
+    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    user_id         UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    title           TEXT NOT NULL,
+    description     TEXT,
+    cuisine         TEXT,
+    difficulty      TEXT,
+    prep_time_min   INT,
+    cook_time_min   INT,
+    servings        INT,
+    image_url       TEXT,
+    ingredients     JSONB NOT NULL DEFAULT '[]',
+    steps           JSONB NOT NULL DEFAULT '[]',
+    tags            JSONB NOT NULL DEFAULT '[]',
+    nutrition       JSONB,
+    source          TEXT NOT NULL DEFAULT 'ai',
+    saved_at        TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE INDEX idx_saved_recipes_user_id ON saved_recipes(user_id);
+CREATE INDEX idx_saved_recipes_saved_at ON saved_recipes(user_id, saved_at DESC);
+
+-- +goose Down
+DROP TABLE saved_recipes;