feat(ui): add dynamic toggle for alternate buffer mode

- Prevents memory access out of bounds crash in yoga-wasm by avoiding synchronous unmounts of history items
- Eliminates duplicated footer artifacts when exiting alternate buffer by ensuring Ink has time to issue erasure codes before swapping terminal buffers
- Fully restores normal buffer scrollback without clipping or duplicating history
- Resolves startup layout rendering bug when alternate buffer is set in config by manually handling terminal transitions instead of letting Ink's alternateBuffer renderer take over