Replace SourceText schema with known-good version (quoted enums incl. portrait-split)

models/SourceText.js

@@ -12,10 +12,10 @@ const sourceTextSchema = new mongoose.Schema({
   sourceLanguage: { type: String, required: true },
 
   sourceType: { 
-      type: String, 
-      enum: [api, manual, practice, tutorial, weekly-practice], 
-      default: manual 
-    },
+    type: String, 
+    enum: ['api', 'manual', 'practice', 'tutorial', 'weekly-practice'], 
+    default: 'manual' 
+  },
   category: {
     type: String,
     enum: ['practice', 'tutorial', 'weekly-practice'],
@@ -30,7 +30,8 @@ const sourceTextSchema = new mongoose.Schema({
   imageAlt: { type: String },
   // Image-only configuration
   imageSize: { type: Number, default: 200 },
-  imageAlignment: { type: String, enum: [left, center, right, portrait-split], default: center },
+  // Add 'portrait-split' for week 4–6 advanced layout (non-breaking, additive)
+  imageAlignment: { type: String, enum: ['left', 'center', 'right', 'portrait-split'], default: 'center' },
   culturalElements: [culturalElementSchema],
   difficulty: { 
     type: String,