feat(udp): speak WSJT-X to Logger32, and lighten Sahara

"sent 1153 bytes to 127.0.0.1:2250" and nothing in Logger32. Both true: the
line the operator screenshotted is titled "Setup additional WSJT/JTDX UDP
sockets", and those receivers take UDP LOGGING PACKETS — the WSJT-X v2
protocol. A bare ADIF record posted to them is dropped without a word.

So there is a new outbound service rather than a change to the existing one:
"WSJT-X logged QSO (Logger32)" sends the same ADIF wrapped in a Logged ADIF
datagram (magic 0xadbccbda, schema 2, type 12), defaulting to port 2250. The
plain-text row stays for JTAlert/GridTracker-style receivers, because the two
really are different wire formats and one row cannot be both.

The id string is "OpsLog", not "WSJT-X": a receiver uses it to tell instances
apart, and impersonating the real thing would make a second WSJT-X
indistinguishable from us.

Tested both ways — the header byte for byte, and a round trip back through our
own ParseWSJT, since that is the same decoding every receiver applies.

Sahara moves to the parchment an operator asked for: page #e6ded0, panels
#f3eee2, toolbars #ded5c4, terracotta #c4501e on the buttons and the focus
ring. Lighter and less saturated than the deep sand it was.

frontend/src/components/SettingsModal.tsx

@@ -413,7 +413,7 @@ const THEME_SWATCH: Record<Exclude<ThemeChoice, 'auto'>, { bg: string; card: str
   'light-warm':    { bg: '#e8dfc9', card: '#faf6ea', accent: '#b8410c' },
   'light-cool':    { bg: '#f4f6f8', card: '#ffffff', accent: '#2563eb' },
   'light-sage':    { bg: '#eef1ec', card: '#f8faf6', accent: '#2f855a' },
-  'sahara':        { bg: '#dcceab', card: '#faf6eb', accent: '#a55f14' },
+  'sahara':        { bg: '#e6ded0', card: '#f3eee2', accent: '#c4501e' },
   'light-nordic':  { bg: '#eef1f7', card: '#ffffff', accent: '#4f46e5' },
   'dim-slate':     { bg: '#343b47', card: '#3d4552', accent: '#fb923c' },
   'dark-warm':     { bg: '#221d18', card: '#2e2820', accent: '#e07a2e' },