chore(tui): remove dead branch cleanup code

- drop unused TUI helpers, test-only layout scaffolding, and stale public debug exports
- remove an unused profiler import and trim test-only coverage for deleted helpers

scripts/profile-tui.py

@@ -30,7 +30,6 @@ import pty
 import select
 import signal
 import sqlite3
-import statistics
 import sys
 import time
 from pathlib import Path