Move and batch spots the way N1MM does

Two differences from N1MM in the spot path, both found by reading Packet.cs.

Randomising moved every CW spot. PacketSpot.Randomize moves a spot only when it
is not a dupe, not a self spot, not on a CQ frequency, is on CW and is not
working split, and Packet skips it altogether for a station passed to another
band. Moving a dupe or a split station makes it harder to find, not easier, so
this now leaves the same ones alone. Whether a station has been worked comes
from the log, so AppSession asks it before moving a spot.

Split needed knowing where a station is listening, which is in the comment. Qsx
reads it by N1MM's rules: QSX, UP, DOWN, DN, U or D, the word standing alone or
after a space, a bare number after QSX meaning kilohertz inside the band and
anything else an offset from the spot, an offset over a hundred kilohertz
refused unless it says QSX, DN70 read as a grid square rather than five down,
and a listening frequency outside the band thrown away.

Spots reached the bandmap one at a time, each one redrawing every window that
watches it. N1MM queues them and flushes the queue once a second, which is what
this does now: the filters and the randomiser run over the batch, and the
bandmap takes it in one call and raises one change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -496,7 +496,13 @@ Three of the filters are worth spelling out:
   call, so `W3LPL` also covers `W3LPL-#`. Nothing is filtered by this.
 - **Randomised frequencies.** Each incoming CW spot is moved thirty or sixty
   hertz either way, which is what N1MM does, so the operator has to find the
-  station by ear. Phone and digital spots are left alone.
+  station by ear. Left where they are: phone and digital spots, stations already
+  worked, stations working split, your own spots, and stations passed to another
+  band — the same list N1MM leaves alone.
+
+Spots wait up to a second before they reach the bandmap, and then go on together.
+N1MM collects them the same way: a skimmer feed sends more spots a minute than
+any window can usefully redraw.
 
 The client speaks telnet properly: it answers the option negotiation instead of
 letting the control bytes turn up in the first lines of text, and it reads the