Reduce timer-tick CPU load by removing per-tick ResizeSMeter and throttling AGC line updates

- Remove ResizeSMeter (Pango font measurement + multiple SetBounds) from 60 Hz timer tick;
  it is still called on actual resize events
- Throttle UpdateAGCLines WDSP API calls from 60 Hz to ~10 Hz (every 6 ticks)
- Optimize spectrum alpha-fix loop: write-only byte access instead of read-modify-write DWORD

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SpectrumView.pas

@@ -696,7 +696,7 @@ procedure TSpectrumView.DrawSpectrum;
 var
   C, GC: TCanvas;
   i, Yp, W, H, GX: Integer;
-  AlphaRow: PCardinal;
+  AlphaPtr: PByte;
   DBmin, DBmax, dB: Double;
   VfoX, X1, X2: Integer;
   TXVfoX, TXX1, TXX2: Integer;
@@ -907,9 +907,12 @@ begin
   FSpectrumBitmap.BeginUpdate(False);
   for i := 0 to H - 1 do
   begin
-    AlphaRow := PCardinal(FSpectrumBitmap.ScanLine[i]);
+    AlphaPtr := PByte(FSpectrumBitmap.ScanLine[i]) + 3;
     for Yp := 0 to W - 1 do
-      AlphaRow[Yp] := AlphaRow[Yp] or $FF000000;
+    begin
+      AlphaPtr^ := $FF;
+      Inc(AlphaPtr, 4);
+    end;
   end;
   FSpectrumBitmap.EndUpdate(False);
 end;