fix(terminal): clear the key-bar latch when the bar goes away

Collapsing the key bar, switching tabs or hiding the panel left an armed
CTRL/ALT latch in place. The latch's only indicator is the highlight on
the bar's own button, so with the bar gone the next soft-keyboard
character was silently wrapped into a control byte — press CTRL, collapse
the bar, type "c", and the shell takes SIGINT with nothing on screen
having suggested it would. The reset now keys off the same `showKeybar`
the bar itself renders from, which subsumes the previous `!isActive` case.

Also drive the panel test at a real viewport width so it pins the
breakpoint rather than a boolean: at exactly 768px the workspace shell is
still desktop, and the panel must agree. Verified the case fails against
the previous `(max-width: 768px)` query.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>