Added command history to ExternalPanelizeDialog:
- history: Vec<String> stores previously-run commands (deduped)
- history_idx: Option<usize> tracks position during navigation
- Up arrow: navigate to older entries (backward through history)
- Down arrow: navigate to newer entries (forward), exit to live input
- Typing any character exits history mode
- Successful command runs push to history (dedup consecutive)
- Render hint shows '↑↓ history' indicator
Self-contained — no changes to Input widget required.
1433 tests pass, zero warnings.
vasilito
30f696e0fa