feat: rename ingredients→products, products→user_products; add barcode/OFF import

- Rename catalog: ingredient/* → product/* (canonical_name, barcode, nutrition per 100g)
- Rename pantry: product/* → userproduct/* (user-owned items with expiry)
- Squash migrations into single 001_initial_schema.sql (clean-db baseline)
- product_categories: add English canonical name column; fix COALESCE in queries
- Remove product_translations: product names are stored in their original language
- Add default_unit_name to product API responses via unit_translations JOIN
- Add cmd/importoff: bulk import from OpenFoodFacts JSONL dump (COPY + ON CONFLICT)
- Diary: support product_id entries alongside dish_id (CHECK num_nonnulls = 1)
- Home: getLoggedCalories joins both recipes and catalog products
- Flutter: rename models/providers/services to match backend rename
- Flutter: add barcode scan flow for diary (mobile_scanner, product_portion_sheet)
- Flutter: localise 6 new keys across 12 languages (barcode scan, portion weight)
- Routes: GET /products/search, GET /products/barcode/{barcode}, /user-products

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

backend/internal/domain/product/openfoodfacts.go

@@ -0,0 +1,84 @@
+package product
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+)
+
+// OpenFoodFacts is the client for the Open Food Facts public API.
+type OpenFoodFacts struct {
+	httpClient *http.Client
+}
+
+// NewOpenFoodFacts creates a new OpenFoodFacts client with the default HTTP client.
+func NewOpenFoodFacts() *OpenFoodFacts {
+	return &OpenFoodFacts{httpClient: &http.Client{}}
+}
+
+// offProduct is the JSON shape returned by the Open Food Facts v2 API.
+type offProduct struct {
+	ProductName string      `json:"product_name"`
+	Brands      string      `json:"brands"`
+	Nutriments  offNutriments `json:"nutriments"`
+}
+
+type offNutriments struct {
+	EnergyKcal100g *float64 `json:"energy-kcal_100g"`
+	Proteins100g   *float64 `json:"proteins_100g"`
+	Fat100g        *float64 `json:"fat_100g"`
+	Carbohydrates100g *float64 `json:"carbohydrates_100g"`
+	Fiber100g      *float64 `json:"fiber_100g"`
+}
+
+type offResponse struct {
+	Status  int        `json:"status"`
+	Product offProduct `json:"product"`
+}
+
+// Fetch retrieves a product from Open Food Facts by barcode.
+// Returns an error if the product is not found or the API call fails.
+func (client *OpenFoodFacts) Fetch(requestContext context.Context, barcode string) (*Product, error) {
+	url := fmt.Sprintf("https://world.openfoodfacts.org/api/v2/product/%s.json", barcode)
+	httpRequest, requestError := http.NewRequestWithContext(requestContext, http.MethodGet, url, nil)
+	if requestError != nil {
+		return nil, fmt.Errorf("build open food facts request: %w", requestError)
+	}
+	httpRequest.Header.Set("User-Agent", "FoodAI/1.0")
+
+	httpResponse, fetchError := client.httpClient.Do(httpRequest)
+	if fetchError != nil {
+		return nil, fmt.Errorf("open food facts request: %w", fetchError)
+	}
+	defer httpResponse.Body.Close()
+
+	if httpResponse.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("open food facts returned status %d for barcode %s", httpResponse.StatusCode, barcode)
+	}
+
+	var offResp offResponse
+	if decodeError := json.NewDecoder(httpResponse.Body).Decode(&offResp); decodeError != nil {
+		return nil, fmt.Errorf("decode open food facts response: %w", decodeError)
+	}
+	if offResp.Status == 0 {
+		return nil, fmt.Errorf("product %s not found in open food facts", barcode)
+	}
+
+	canonicalName := offResp.Product.ProductName
+	if canonicalName == "" {
+		canonicalName = barcode // Fall back to barcode as canonical name
+	}
+
+	barcodeValue := barcode
+	catalogProduct := &Product{
+		CanonicalName:   canonicalName,
+		Barcode:         &barcodeValue,
+		CaloriesPer100g: offResp.Product.Nutriments.EnergyKcal100g,
+		ProteinPer100g:  offResp.Product.Nutriments.Proteins100g,
+		FatPer100g:      offResp.Product.Nutriments.Fat100g,
+		CarbsPer100g:    offResp.Product.Nutriments.Carbohydrates100g,
+		FiberPer100g:    offResp.Product.Nutriments.Fiber100g,
+	}
+	return catalogProduct, nil
+}