fix(2meet-data-optimizer): keep the audit trail of mode changes and snapshot deletions

- TMDO_Logger::notice() is always written to the error log (it had no
  callers); bridge_mode_changed and snapshot_deleted use it. Since PR-095
  info() is silent without WP_DEBUG_LOG, which left no record of who switched
  a mode or deleted a snapshot (security review L1)
- Verify: LoggerTest (notice always logged, info gated), unit 703,
  integration 585, phpcs, stan
- PR: PR-113 (2.3 acceptance security review)

includes/engine/class-tmdo-mode-manager.php

@@ -159,7 +159,7 @@ final class TMDO_Mode_Manager {
 		$entered[ $entity_type ] = time();
 		update_option( self::OPT_ENTERED_AT, $entered, false );
 
-		TMDO_Logger::info(
+		TMDO_Logger::notice(
 			'bridge_mode_changed',
 			array(
 				'entity_type' => $entity_type,