nutrition: detect recipe refs in ingredients, show in edit UI with multiplier

Skip embedding matching for anchor-tag ingredients that reference other
recipes. Instead, mark them with recipeRef/recipeRefMultiplier fields so
their nutrition is resolved via resolveReferencedNutrition with a
user-configurable fraction. The edit UI shows these as teal REF badges
with an editable "Anteil" input.

src/models/Recipe.ts

@@ -180,6 +180,8 @@ const RecipeSchema = new mongoose.Schema(
        unitConversionSource: { type: String, enum: ['direct', 'density', 'usda_portion', 'estimate', 'manual', 'none'] },
        manuallyEdited: { type: Boolean, default: false },
        excluded: { type: Boolean, default: false },
+       recipeRef: { type: String },
+       recipeRefMultiplier: { type: Number, default: 1 },
      }],
 
      // Translation metadata for tracking changes