fix: Ensure migration_state updates are committed to database

The _update_migration_state() method was using pg_conn.execute() which has
its own connection management. This could cause issues with transaction
handling when called at end of migration.

Changed to use explicit cursor with guaranteed commit:
- Use pg_conn.connection.cursor() to get a direct cursor
- Execute the INSERT ... ON CONFLICT query
- Explicitly call pg_conn.connection.commit()
- This matches the pattern used in other parts of the code

This ensures that final migration state (completed status, final counts)
are properly persisted to the database.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/migrator/full_migration.py

@@ -255,8 +255,7 @@ class FullMigrator:
 
         # Update PostgreSQL migration_state table
         try:
-            # Use COALESCE to handle both insert (first time) and update (resume)
+            with pg_conn.connection.cursor() as cursor:
-            # For resume: total_rows_migrated will be the full accumulated count
                 query = f"""
                     INSERT INTO migration_state
                     (table_name, last_migrated_timestamp, last_migrated_id, total_rows_migrated, migration_completed_at, status)
@@ -268,7 +267,7 @@ class FullMigrator:
                         migration_completed_at = EXCLUDED.migration_completed_at,
                         status = EXCLUDED.status
                 """
-            pg_conn.execute(
+                cursor.execute(
                     query,
                     (
                         pg_table,
@@ -279,6 +278,7 @@ class FullMigrator:
                         status
                     )
                 )
+                pg_conn.connection.commit()
             logger.debug(f"Migration state updated: {rows_migrated} rows total, last_id={last_id}, status={status}")
         except Exception as e:
             logger.warning(f"Failed to update migration state in PostgreSQL: {e}")