Optimize CPU waterfall/spectrum rendering

WaterfallView: drop per-frame TLazIntfImage + LoadFromIntfImage (device
bitmap recreation + full pixel-format conversion every frame). Write
pixels directly into the bitmap via BeginUpdate/ScanLine like
SpectrumView already does, with platform-native byte order (ARGB on
Cocoa, BGRA elsewhere).

Replace per-pixel float colorization with a 512-entry dB->color LUT
rebuilt only when WfLow/WfHigh/theme change beyond a small threshold.

Turn the bitmap itself into a ring buffer: each frame builds a single
new row and writes one ScanLine; scrolling is done at paint time via two
CopyRect calls. Removes both full-frame passes per frame (image memmove
+ buffer->bitmap copy), cutting per-frame cost from O(W*H) to O(W). TX
mode preserved by leaving out-of-span columns untouched in the row buf.

SpectrumView: rewrite the per-frame alpha-restore pass from a strided
per-byte loop to a sequential per-dword OR with the alpha mask
(bit-identical output, sequential memory access).

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

SpectrumView.pas

@@ -722,7 +722,8 @@ procedure TSpectrumView.DrawSpectrum;
 var
   C, GC: TCanvas;
   i, Yp, W, H, GX: Integer;
-  AlphaPtr: PByte;
+  RowLW: PLongWord;
+  AMask: LongWord;
   DBmin, DBmax, dB: Double;
   VfoX, X1, X2: Integer;
   TXVfoX, TXX1, TXX2: Integer;
@@ -930,18 +931,22 @@ begin
   if Assigned(FVfoOverlay) then
     FVfoOverlay.DrawOverlay(FSpectrumBitmap, W, H);
 
+  // Восстанавливаем непрозрачность: Canvas-операции (текст/линии со сглаживанием)
+  // могли занулить альфу. OR маской выставляет альфу в $FF, RGB не меняя.
+{$IFDEF DARWIN}
+  AMask := $000000FF;   // ARGB: альфа в байте 0
+{$ELSE}
+  AMask := $FF000000;   // BGRA: альфа в байте 3
+{$ENDIF}
   FSpectrumBitmap.BeginUpdate(False);
   for i := 0 to H - 1 do
   begin
-{$IFDEF DARWIN}
-    AlphaPtr := PByte(FSpectrumBitmap.ScanLine[i]);       // ARGB: alpha at byte 0
-{$ELSE}
-    AlphaPtr := PByte(FSpectrumBitmap.ScanLine[i]) + 3;   // BGRA: alpha at byte 3
-{$ENDIF}
+    RowLW := PLongWord(FSpectrumBitmap.ScanLine[i]);
+    if RowLW = nil then Continue;
     for Yp := 0 to W - 1 do
     begin
-      AlphaPtr^ := $FF;
-      Inc(AlphaPtr, 4);
+      RowLW^ := RowLW^ or AMask;
+      Inc(RowLW);
     end;
   end;
   FSpectrumBitmap.EndUpdate(False);