fix: Update migration state with final count when migration completes

When migration finishes, we need to update migration_state with:
1. The final actual row count from PostgreSQL
2. The final last_migrated_id (MAX(id) from the table)
3. Mark status as 'completed' (handled by _update_migration_state)

Previously, the final state update was missing, so migration_state
was left with stale data from the periodic updates.

Now _update_migration_state is called at the end to record the
authoritative final state.

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

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

src/migrator/full_migration.py

@@ -161,6 +161,23 @@ class FullMigrator:
 
                     # Get final actual count from PostgreSQL
                     final_count = pg_conn.get_row_count(pg_table)
+
+                    # Update migration state with final count and mark as completed
+                    # Get the actual last ID from the table
+                    try:
+                        with pg_conn.connection.cursor() as cursor:
+                            cursor.execute(
+                                f"SELECT MAX(id) FROM {pg_table}"
+                            )
+                            result = cursor.fetchone()
+                            final_last_id = result[0] if result and result[0] else None
+                    except Exception:
+                        final_last_id = None
+
+                    self._update_migration_state(
+                        pg_conn, final_count, final_last_id, migration_start_time
+                    )
+
                     logger.info(
                         f"✓ Migration complete: {final_count} total rows in {pg_table}"
                     )