WIP: TX implementation — per-device settings, separate analyzer, sound-card mic

- Settings: TTXSettings record + LoadTX/SaveTX, JSON section "tx" per MAC
- WDSPEngine: separate TX_DISP_ID analyzer with own FFT/Window/Det/Avg
  parameters, ApplyTXAnalyzerSettings + setters
- WDSPEngine: full TX chain setters (Filter/Compressor/Leveler/ALC/
  PhaseRot/EQ/AMCarrier/FM/CTCSS) + ApplyTXChainSettings
- WDSPEngine: ProcessTXBlock now feeds TX analyzer in DISPLAY_BLOCK_SIZE
  chunks (was passing whole FTXOut → analyzer ignored most of it)
- WDSPEngine: ActiveDisplayID switches RX/TX in UpdateSpectrum
- WDSPEngine: RX audio muted while TX active to avoid local feedback
- WDSPEngine: default EQ frequencies in Create (zero freqs broke TX chain)
- WDSPEngine: PushTXMicSampleD + OnPullMicSamples for sound-card path
- AudioInput: Available counter for non-blocking pull
- MainForm: PullSoundCardMic, BuildMicLineSelectByte, SendDUCSpecific
  with mic bias/boost/line/PTT bits, OnTXSettingsChange
- MainForm: auto-switch MicSource on TX device select, TX diagnostic
  in StatusBar panel [5]
- SettingsForm: new Transmit nav page with Microphone, Filter, Dynamic
  processing, EQ, AM/FM/CTCSS, TX Display sections

NOT YET WORKING: sound-card mic produces ring activity but signal still
not visible on TX spectrum/waterfall — needs further investigation.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

AudioInput.pas

@@ -132,6 +132,9 @@ type
     // Читает следующий моно-сэмпл из кольцевого буфера.
     // Возвращает 0.0 если буфер пуст.
     function  ReadSample: Double;
+    // Сколько сэмплов реально лежит в ring буфере (0..MY_MIC_RING_SIZE-1).
+    // Использовать для чтения только доступных данных без пуш-тишины.
+    function  Available: Integer;
 
     property IsOpen:      Boolean read FOpen;
     property LastError:   string  read GetLastError;
@@ -534,4 +537,13 @@ begin
   FOutPt := newpt;
 end;
 
+function TAudioInput.Available: Integer;
+var d: Integer;
+begin
+  // Считаем сколько непрочитанных сэмплов между OutPt (читатель) и InPt (писатель).
+  d := FInPt - FOutPt;
+  if d < 0 then d := d + MY_MIC_RING_SIZE;
+  Result := d;
+end;
+
 end.