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>

MainForm.pas

@@ -478,6 +478,7 @@ type
     procedure OnAlexSettingsChange(const A: TAlexSettings);
     procedure OnXvtrSettingsChange(const X: TXvtrSettings);
     procedure PushXvtrToWeb;
+    procedure PushRatePresetsToWeb;   // backend sample-rate пресеты → web
     // XVTR helpers
     function  FindXvtrIdxForFreq(FreqHz: Double): Integer;
     function  XvtrTranslate(VisibleHz: Double): Double;
@@ -882,6 +883,7 @@ begin
   if FWebEnabled then FWebServer.Start;
   PushXvtrToWeb;
   PushDeviceListToWeb;   // saved-устройства сразу видны web-overlay
+  PushRatePresetsToWeb;  // дефолтный бэкенд до connect; перезапишется на смене
   FillChar(FCATLastGlobal, SizeOf(FCATLastGlobal), 0);
   FCATLastGlobal.CATTcpPort := 19090;
   for i := 0 to 3 do
@@ -3678,12 +3680,11 @@ begin
   Caps := FController.BackendCaps;
   if Assigned(FSampleRateOverlay) then
   begin
-    if (Caps.SampleRateMode = srmContinuous) and (Length(Caps.RatePresets) > 0) then
-      FSampleRateOverlay.SetRatePresets(Caps.RatePresets)
-    else
-      FSampleRateOverlay.SetRatePresetsDefault;   // HPSDR 48k..1536k
+    // Единый источник — контроллер (caps бэкенда). UI больше не владеет списком.
+    FSampleRateOverlay.SetRatePresets(FController.SampleRatePresets);
     FSampleRateOverlay.SetCurrentRate(FController.FSampleRate);
   end;
+  PushRatePresetsToWeb;   // тот же источник зеркалим в web-морду
 
   // Отдельный Pluto RF-AGC блок под AGC: показываем и сдвигаем панели ниже.
   LayoutLeftPanel(Caps.HasHWGain);
@@ -5366,6 +5367,14 @@ begin
   end;
 end;
 
+procedure TMainForm.PushRatePresetsToWeb;
+// Пресеты sample-rate бэкенда → web (HPSDR/Pluto разные). Единый источник —
+// FController.SampleRatePresets, как и для desktop-оверлея.
+begin
+  if FWebServer = nil then Exit;
+  FWebServer.SetRatePresets(FController.SampleRatePresets);
+end;
+
 procedure TMainForm.PushXvtrToWeb;
 var
   Arr: TWebXvtrArray;