fix(tmux-subagent): move 'cleanup complete' log back to cleanup() method

The log line was misplaced at the end of sweepStaleIsolatedSessionsOnce
where it said 'cleanup complete' after the stale sweep, which was
misleading. Per Oracle review.

src/features/tmux-subagent/manager.ts

@@ -989,6 +989,8 @@ export class TmuxSessionManager {
     }
 
     this.staleSweepCompleted = false
+
+    log("[tmux-session-manager] cleanup complete")
   }
 
   private async sweepStaleIsolatedSessionsOnce(): Promise<void> {
@@ -1009,7 +1011,5 @@ export class TmuxSessionManager {
         error: String(error),
       })
     }
-
-    log("[tmux-session-manager] cleanup complete")
   }
 }