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/gemini/client.go

@@ -0,0 +1,81 @@
+package gemini
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+const (
+	// Groq — OpenAI-compatible API, free tier, no billing required.
+	groqAPIURL = "https://api.groq.com/openai/v1/chat/completions"
+	groqModel  = "llama-3.3-70b-versatile"
+	maxRetries = 3
+)
+
+// Client is an HTTP client for the Groq LLM API (OpenAI-compatible).
+type Client struct {
+	apiKey     string
+	httpClient *http.Client
+}
+
+// NewClient creates a new Client.
+func NewClient(apiKey string) *Client {
+	return &Client{
+		apiKey: apiKey,
+		httpClient: &http.Client{
+			Timeout: 60 * time.Second,
+		},
+	}
+}
+
+// generateContent sends a user prompt to Groq and returns the assistant text.
+func (c *Client) generateContent(ctx context.Context, messages []map[string]string) (string, error) {
+	body := map[string]any{
+		"model":       groqModel,
+		"temperature": 0.7,
+		"messages":    messages,
+	}
+
+	bodyBytes, err := json.Marshal(body)
+	if err != nil {
+		return "", fmt.Errorf("marshal request: %w", err)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, groqAPIURL, bytes.NewReader(bodyBytes))
+	if err != nil {
+		return "", fmt.Errorf("create request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Authorization", "Bearer "+c.apiKey)
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("send request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		raw, _ := io.ReadAll(resp.Body)
+		return "", fmt.Errorf("groq API error %d: %s", resp.StatusCode, string(raw))
+	}
+
+	var result struct {
+		Choices []struct {
+			Message struct {
+				Content string `json:"content"`
+			} `json:"message"`
+		} `json:"choices"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+		return "", fmt.Errorf("decode response: %w", err)
+	}
+	if len(result.Choices) == 0 {
+		return "", fmt.Errorf("empty response from Groq")
+	}
+	return result.Choices[0].Message.Content, nil
+}