tui: TERMINAL_RESTORE slot Vec never reclaims trailing None entries

[Ariestar]

CodeRabbit nitpick on PR #73 (panic-hook-global), src/tui/panic.rs.

register_restore only pushes; RestoreRegistration::drop only writes None at the index. The Vec never shrinks, so a process that opens and closes many TUI sessions on the same thread accumulates one entry per session. The leak is small but unbounded.

Suggested direction: in RestoreRegistration::drop, truncate trailing None entries after clearing the slot; live indices stay stable.