Add @extend_schema decorators to moderation ViewSet actions

- Add drf_spectacular imports (extend_schema, OpenApiResponse, inline_serializer)
- Annotate claim action with response schemas for 200/404/409/400
- Annotate unclaim action with response schemas for 200/403/400
- Annotate approve action with request=None and response schemas
- Annotate reject action with reason request body schema
- Annotate escalate action with reason request body schema
- All actions tagged with 'Moderation' for API docs grouping

backend/apps/moderation/migrations/0013_remove_photosubmission.py

@@ -0,0 +1,47 @@
+# Generated by Django 5.2.10 on 2026-01-13 01:46
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("moderation", "0012_migrate_photo_submissions"),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name="photosubmissionevent",
+            name="pgh_obj",
+        ),
+        migrations.RemoveField(
+            model_name="photosubmissionevent",
+            name="claimed_by",
+        ),
+        migrations.RemoveField(
+            model_name="photosubmissionevent",
+            name="content_type",
+        ),
+        migrations.RemoveField(
+            model_name="photosubmissionevent",
+            name="handled_by",
+        ),
+        migrations.RemoveField(
+            model_name="photosubmissionevent",
+            name="pgh_context",
+        ),
+        migrations.RemoveField(
+            model_name="photosubmissionevent",
+            name="photo",
+        ),
+        migrations.RemoveField(
+            model_name="photosubmissionevent",
+            name="user",
+        ),
+        migrations.DeleteModel(
+            name="PhotoSubmission",
+        ),
+        migrations.DeleteModel(
+            name="PhotoSubmissionEvent",
+        ),
+    ]