fix(build): bundle bettercam/dxcam/windows-capture in installer

The Windows installer was only shipping mss as a screen-capture
backend, so EngineRegistry.get_available_engines() reported just
['mss', 'camera', 'demo'] on installed builds. Picture sources
configured to use bettercam/dxcam/wgc were rejected at the
test/ws handshake with HTTP 403 (close-before-accept on
"Engine '<x>' not available").

Add the three Windows screen-capture wheels to WIN_DEPS so the
installer build matches a 'pip install -e .' dev environment.

build-dist-windows.sh

@@ -213,6 +213,10 @@ WIN_DEPS=(
     # System tray (Pillow needed by pystray for tray icon)
     "pystray>=0.19.0"
     "Pillow>=10.4.0"
+    # Windows screen capture engines (mss is the only fallback without these)
+    "dxcam>=0.0.5"
+    "bettercam>=1.0.0"
+    "windows-capture>=1.5.0"
 )
 
 # Download cross-platform deps (prefer binary, allow source for pure Python)