A restarted pane keeps the old program's scroll region, origin and insert modes and charset #66

Term::modes_off (added in #64) resets the mouse, paste, cursor, keypad, alternate-screen and focus modes but not the scroll region (DECSTBM), origin mode (?6), insert mode (4) or the G0 charset. A TUI killed mid-redraw by Isolation… → [r] leaves the new shell confined to part of the screen or printing line-drawing glyphs. Found in review of #64; the same reset runs when a command leaves and the shell comes back, and that path has no test.

Also: requeue keeps a stale via on a message, so a message requeued after a typed hand-over is left out of UNREAD while in flight (#61 review).