Audit fixes 2026-10-03: seed keeps admin edits, plan cache, refresh limit, payment and tutor guards

- seed_content no longer undoes admin work: a SeedRecord ledger (content/seed_sync.py)
  stops deleted/renamed/re-worded content from being recreated and keeps admin-edited
  lesson text; new rows in the seed files still arrive (migration content.0010)
- plan list cache is invalidated on Plan save (receiver used a stale 'v1' key)
- token refresh per-IP cap 30/hour -> 600/hour (TOKEN_REFRESH_IP_RATE)
- a failed gateway result only changes a pending order (forged NOK no longer
  overwrites refunded/canceled)
- tutor gets the correct answer only after the student has answered
- support reply notification moved to a TicketMessage post_save signal
- global daily cap on paid AI questions (AI_GLOBAL_DAILY_MAX, default 3000)
- Bazaar verify uses only the order's SKU; bazaar orders require a SKU
- /api/health warns on the committed signing key; deploy.sh saves local commits;
  400 for bad ?unit= / ?period=; account delete keeps the referrer's Conversion
- earlier today: no stub answers outside DEBUG, ?grade= removed, logged fallbacks

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

content/migrations/0010_seedrecord.py

@@ -0,0 +1,23 @@
+# Generated by Django 5.2.17 on 2026-10-03 08:41
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('content', '0009_usernodecompletion'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='SeedRecord',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('key', models.CharField(max_length=40, unique=True)),
+                ('kind', models.CharField(max_length=10)),
+                ('value', models.CharField(blank=True, max_length=40)),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+            ],
+        ),
+    ]