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/userproduct/entity.go

@@ -0,0 +1,41 @@
+package userproduct
+
+import "time"
+
+// UserProduct is a user's food item in their pantry.
+type UserProduct struct {
+	ID               string    `json:"id"`
+	UserID           string    `json:"user_id"`
+	PrimaryProductID *string   `json:"primary_product_id"`
+	Name             string    `json:"name"`
+	Quantity         float64   `json:"quantity"`
+	Unit             string    `json:"unit"`
+	Category         *string   `json:"category"`
+	StorageDays      int       `json:"storage_days"`
+	AddedAt          time.Time `json:"added_at"`
+	ExpiresAt        time.Time `json:"expires_at"`
+	DaysLeft         int       `json:"days_left"`
+	ExpiringSoon     bool      `json:"expiring_soon"`
+}
+
+// CreateRequest is the body for POST /user-products.
+type CreateRequest struct {
+	PrimaryProductID *string  `json:"primary_product_id"`
+	// Accept "mapping_id" as a legacy alias for backward compatibility.
+	MappingID        *string  `json:"mapping_id"`
+	Name             string   `json:"name"`
+	Quantity         float64  `json:"quantity"`
+	Unit             string   `json:"unit"`
+	Category         *string  `json:"category"`
+	StorageDays      int      `json:"storage_days"`
+}
+
+// UpdateRequest is the body for PUT /user-products/{id}.
+// All fields are optional (nil = keep existing value).
+type UpdateRequest struct {
+	Name        *string  `json:"name"`
+	Quantity    *float64 `json:"quantity"`
+	Unit        *string  `json:"unit"`
+	Category    *string  `json:"category"`
+	StorageDays *int     `json:"storage_days"`
+}