Signed payment links, hashed refresh tokens, login-only leaderboard, load test tools

- /api/payment/orders/{id}/pay requires the short-lived signature that paymentUrl carries;
  without it (or with another order's) it is the same 404 as an unknown order
- Session.refresh_token stores the SHA-256 of the token; migration accounts.0007 hashes the
  existing rows so tokens clients already hold keep working
- /api/leaderboard requires a token (guests have one); names of children were scrapable
- RAG mock only for `manage.py test`, not any command with an argument named "test"
- tools/loadtest: user factory, load generator, fake GapGPT+Qdrant, with method notes
- security-before-production.md lists only open items; closed ones become a guards table
  with the tests that hold them. Comments describe current behaviour, not history

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

accounts/migrations/0007_hash_refresh_tokens.py

@@ -0,0 +1,28 @@
+"""
+Session.refresh_token از این به بعد هشِ SHA-256 است (accounts/models.py، hash_refresh_token).
+ردیف‌های موجود هش می‌شوند تا توکن‌هایی که کلاینت‌ها در دست دارند همچنان کار کنند. از هش نمی‌شود
+خودِ توکن را ساخت؛ برگرداندنِ این migration هش‌ها را سرِ جایشان می‌گذارد و کدِ قبلی آن‌ها را
+نمی‌شناسد، یعنی هر کاربر یک بار دوباره وارد می‌شود.
+"""
+import hashlib
+
+from django.db import migrations
+
+
+def hash_existing(apps, schema_editor):
+    Session = apps.get_model('accounts', 'Session')
+    # اول مادی کردن، بعد نوشتن: کرسرِ بازِ SQLite وسطِ حلقه‌ی نوشتن قفل می‌سازد (CLAUDE.md).
+    rows = list(Session.objects.values_list('id', 'refresh_token'))
+    for pk, raw in rows:
+        Session.objects.filter(pk=pk).update(refresh_token=hashlib.sha256(raw.encode()).hexdigest())
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('accounts', '0006_profile_birth_date_drop_parent_phone'),
+    ]
+
+    operations = [
+        migrations.RunPython(hash_existing, migrations.RunPython.noop),
+    ]