Add migration to drop speakers app database tables

Creates core migration 0010_remove_speakers_tables.py that:
- Drops all database tables from the removed speakers app
- Handles table dependencies correctly (CASCADE)
- Drops tables in order: junction tables, then FK tables, then base tables
- Is irreversible (requires backup to rollback)

Tables dropped:
- speakers_session_speakers (M2M junction table)
- speakers_session
- speakers_speaker
- speakers_room
- speakers_talkspage
- speakers_speakerspage

This migration should be run on production before deploying the code
that removes the speakers app from INSTALLED_APPS.

Author: matrixise

pythonie/core/migrations/0010_remove_speakers_tables.py

@@ -0,0 +1,55 @@
+# Generated manually to remove speakers app tables
+
+from django.db import migrations
+
+
+def drop_speakers_tables(apps, schema_editor):
+    """
+    Drop all tables from the removed speakers app.
+
+    This migration removes tables that were part of the speakers app which
+    has been completely removed from the codebase. The tables are dropped
+    in order to handle foreign key constraints properly.
+    """
+    # We can't use apps.get_model() here since the speakers app is removed
+    # Instead, we use raw SQL to drop the tables
+    with schema_editor.connection.cursor() as cursor:
+        # Drop tables in reverse dependency order
+        # First drop junction tables (M2M relationships)
+        cursor.execute("DROP TABLE IF EXISTS speakers_session_speakers CASCADE")
+
+        # Then drop tables with foreign keys
+        cursor.execute("DROP TABLE IF EXISTS speakers_session CASCADE")
+        cursor.execute("DROP TABLE IF EXISTS speakers_speaker CASCADE")
+
+        # Drop remaining tables
+        cursor.execute("DROP TABLE IF EXISTS speakers_room CASCADE")
+        cursor.execute("DROP TABLE IF EXISTS speakers_talkspage CASCADE")
+        cursor.execute("DROP TABLE IF EXISTS speakers_speakerspage CASCADE")
+
+
+def reverse_drop_speakers_tables(apps, schema_editor):
+    """
+    This migration is irreversible.
+
+    If you need to rollback, restore from a database backup taken before
+    running this migration.
+    """
+    raise RuntimeError(
+        "This migration cannot be reversed. "
+        "The speakers app and its data have been permanently removed. "
+        "Restore from a backup if you need to recover."
+    )
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("core", "0009_auto_20160703_0857"),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            drop_speakers_tables,
+            reverse_drop_speakers_tables,
+        ),
+    ]