The 4s reconcile tick called Apply(), which did Rows.Clear() + refill on
every tick -- resetting the user's scroll position and selection while
they're mid-read, exactly what the overlay exists to avoid.
Reconcile granularly instead: find the overlap between the previous and
latest snapshot (the ring buffer is append-mostly, evicting from the
front as entries age out of the 30-min window), trim rows for evicted
entries off the tail, and insert new entries at the head. A tick with no
change now leaves Rows untouched. The WarnErrorOnly toggle still goes
through the full Apply() rebuild, unchanged.
Reverses row order in LogVisualizerViewModel.Apply() so the most recent
entry sits at index 0, matching the "what just happened" use case;
filtering and refresh are unaffected since the reversal happens after
the warn/error filter is applied.
