Squash blog migrations: combine introduction and page_links fields

- Remove separate migration files 0030 and 0031
- Create single migration 0030_blogindexpage_introduction_and_page_links
- Combines both field additions into one migration as requested in PR feedback

Author: kevinhowbrook

tbx/blog/migrations/0030_adds_introduction_field.py

@@ -1,16 +1,21 @@
 # Generated by Django 5.2.5 on 2025-10-22 09:34
 
-from django.db import migrations
+from django.db import migrations, models
 
 import tbx.core.utils.fields
 
 
 class Migration(migrations.Migration):
     dependencies = [
-        ("blog", "0030_adds_introduction_field"),
+        ("blog", "0029_relatedblogpage"),
     ]
 
     operations = [
+        migrations.AddField(
+            model_name="blogindexpage",
+            name="introduction",
+            field=models.TextField(blank=True),
+        ),
         migrations.AddField(
             model_name="blogindexpage",
             name="page_links",