feat: unify sample-rate presets across desktop + web UIs

Sample-rate (span) presets were duplicated in three places and none was
authoritative: HPSDR set hardcoded in the desktop overlay (SPAN_RATES),
Pluto set in backend caps, and a separate hardcoded list in the web JS.
The web showed HPSDR rates even on Pluto, and the web adapter silently
dropped any rate outside a hardcoded HPSDR whitelist (so Pluto-only rates
like 960k/2304k never switched).

Single source of truth = backend caps -> controller:
- HPSDRNetwork.Caps now fills RatePresets [48k..1536k] (was nil).
- RadioBackend: named type TBackendRateArray.
- TRadioController.SampleRatePresets returns BackendCaps.RatePresets.

Both UIs derive from it:
- Desktop: ApplyBackendCapsToUI always feeds the overlay from
  SampleRatePresets (overlay no longer owns the HPSDR list).
- Web: WebServer.SetRatePresets + rate_presets in state JSON; hosts
  (daemon OnState/startup, GUI ApplyBackendCapsToUI/startup) push
  SampleRatePresets; JS builds span buttons dynamically from it.
- WebAdapter.SyncSpan validates against SampleRatePresets instead of a
  hardcoded whitelist, so any backend rate is accepted.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ewsdrd.lpr

@@ -55,6 +55,7 @@ type
     procedure ConnectTo(const Dev: THPSDRDevice);
     procedure PushDeviceList;
     procedure PushXvtr;
+    procedure PushRatePresets;   // sample-rate пресеты бэкенда → web
     // Входящие web-команды (из WS-потока): запоминаем параметр и маршалим в Sync*.
     procedure WebRun(On_: Boolean);
     procedure WebConnect(const IP: string);
@@ -196,7 +197,7 @@ begin
   // выходные web-списки, которых нет в периодическом PushState.
   case Field of
     rfDeviceList: PushDeviceList;             // discovered обновился
-    rfXvtr, rfDevice: begin PushXvtr; PushDeviceList; end;  // connect / xvtr-смена
+    rfXvtr, rfDevice: begin PushXvtr; PushDeviceList; PushRatePresets; end;  // connect / xvtr / backend
   end;
 end;
 
@@ -291,6 +292,11 @@ begin
   FWeb.SetXvtrBands(Arr, FCtrl.FCurrentXvtr);
 end;
 
+procedure THeadlessHost.PushRatePresets;
+begin
+  FWeb.SetRatePresets(FCtrl.SampleRatePresets);
+end;
+
 // --- Входящие web-команды (WS-поток) → маршалинг в главный поток ---
 
 procedure THeadlessHost.WebRun(On_: Boolean);
@@ -382,6 +388,7 @@ begin
   end;
   Log('Web control on http://' + WebCfg.BindAddr + ':' + IntToStr(WebCfg.Port));
   PushDeviceList;
+  PushRatePresets;   // дефолтный бэкенд (HPSDR) до connect; перезапишется на смене
 
   // FRunning ставим ДО autostart: первый WDSP-open может занять время, и если за
   // него прилетит SIGINT (RequestStop→FRunning:=False), цикл сразу завершится, а