feat(udp): custom outbound messages — a trigger, a template, UDP or a URL

The hard-coded emitters each speak one published format at one fixed moment.
This is the escape hatch, and it exists mainly for antenna switches: they are
driven by a URL, and the band change is the trigger they want.

Four triggers, each carrying its own field set: band change (the RADIO's band,
not the entry form — a switch follows the rig, not what is being typed), QSO
logged, rotator command and callsign lookup. The panel prints the fields the
selected trigger can fill, which is the point of the whole thing: a placeholder
the trigger does not carry renders as nothing, and without the list an operator
writes {freq} on a band change and has no way to learn why the switch never
moved.

Three things the panel cannot show, handled here:

  - Escaping. A URL needs every value percent-encoded; a UDP payload must not
    be touched. The first portable callsign, F4BPO/P, puts a path separator in
    the middle of a query string otherwise — it works on the bench and fails on
    the air.
  - Blocking. An HTTP call to a switch that is unplugged would otherwise sit
    for the operating system's timeout, on the path of a band change. It runs
    in the background with a 3 s limit.
  - Silence. A switch answering 404 after a firmware update fails exactly like
    success looks from here, so the status code is logged, throttled per row.

The rotator trigger hooks the COMMAND rather than the SP/LP buttons, so the
compass and a spot click fire it too, and the path ("SP"/"LP") is passed
through because an azimuth alone cannot say which was taken — 137° is short
path to one station and long to another.

Credentials in a URL are stored as typed. That is the operator's call, on the
grounds that this is LAN gear, and the hint in the panel says so.

frontend/src/App.tsx

@@ -17,6 +17,7 @@ import {
   SMTPConfigured, SendLogToDeveloper,
   WorkedBefore,
   SetCompactMode, SetCompactHeight,
+  RotatorGoToPath,
   GetCATState, SetCATFrequency, SetCATMode, SwitchCATRig, FlexApplyBandAntenna, FlexApplyBandPower,
   GetSecretStatus, UnlockSecrets,
   RefreshCtyDat, DownloadAllReferenceLists,
@@ -5370,13 +5371,15 @@ export default function App() {
             {(() => {
               const p = dxPath;
               const disabled = !p;
-              const goto = (az: number) => RotatorGoTo(Math.round(az), -1).catch((err) => setError(String(err?.message ?? err)));
+              // The path is passed through so a custom outbound row can say which
+              // bearing was taken — 137° is short path to one station and long to another.
+              const goto = (az: number, path: 'SP' | 'LP') => RotatorGoToPath(Math.round(az), -1, path).catch((err) => setError(String(err?.message ?? err)));
               return (
                 <div className="inline-flex items-center rounded-full border border-info-border bg-info-muted overflow-hidden text-[11px] font-mono font-semibold">
                   <button
                     type="button"
                     disabled={disabled}
-                    onClick={() => p && goto(p.bearingShort)}
+                    onClick={() => p && goto(p.bearingShort, 'SP')}
                     title={p
                       ? `Rotate short-path · ${Math.round(p.distanceShort).toLocaleString()} km`
                       : (station.my_grid ? 'No remote grid' : 'Set your station grid in Preferences')}
@@ -5393,7 +5396,7 @@ export default function App() {
                   <button
                     type="button"
                     disabled={disabled}
-                    onClick={() => p && goto(p.bearingLong)}
+                    onClick={() => p && goto(p.bearingLong, 'LP')}
                     title={p ? `Rotate long-path · ${Math.round(p.distanceLong).toLocaleString()} km` : ''}
                     className={cn(
                       'px-1.5 py-0.5 border-l border-info-border text-[10px] transition-colors',