fix: stop force-killing apps during uninstall (Mac app parity)

force_kill_app no longer escalates past the graceful Quit Apple Event.
The pkill, pkill -9, and sudo pkill -9 ladder is removed: force-killing
risks losing the app's unsaved work and leaving half-written state on
disk. A still-running app is reported via return 1; the caller already
warns the user and proceeds, since macOS allows removing a running
bundle. This matches the Mac app, which dropped the ladder earlier.