Debug logging disproved the previous "recent append perturbs GetFocus"
theory - one spurious jump fired 7.67s after the last append. The real
pattern: GetFocus() reports "not focused" for a single poll tick now
and then even while the user never left the window, and that lone blip
was enough for the very next tick to be read as "just switched to the
window," triggering a jump on practically every incoming line.
Now requires 3 consecutive unfocused poll ticks (~0.6s) before the next
focused tick counts as a genuine switch, filtering out single-tick
noise from MUSHclient's own UI thread. Removed the now-unused
last_append_clock tracking from the previous (wrong) fix attempt.
466be8a544