Terminal control-mode tracking centralized into a mode-set class

Terminal escape-sequence state, covering bracketed paste, theme reports, extended keys, alt screen, alt-screen keys, mouse tracking, background color queries, and focus events, is now tracked by a single ordered mode-set class with set/reset/suspend/resume operations, replacing ad hoc raw writes scattered through the render and raw-mode code. This is an internal restructuring of how terminal modes are entered, exited, and restored (for example on suspend/resume when shelling out or exiting) rather than a user-facing change.