Fix vertical offset when capturing the secondary display

The first ScreenCaptureKit Y-flip used the wrong reference edges, shifting
cropped selections on displays below the main screen. Convert each selection
per-display as scY = appKitY - NSScreen.maxY + SCDisplay.maxY, which
matches both the main and secondary displays.

💘 Generated with Crush

Assisted-by: Crush:deepseek-v4-flash-0731

build-app.sh

@@ -108,9 +108,9 @@ cat > "$APP/Contents/Info.plist" <<'PLIST'
     <key>CFBundleIconFile</key>
     <string>Icon</string>
     <key>CFBundleShortVersionString</key>
-    <string>1.1.7</string>
+    <string>1.1.8</string>
     <key>CFBundleVersion</key>
-    <string>17</string>
+    <string>18</string>
     <key>LSUIElement</key>
     <true/>
     <key>NSHighResolutionCapable</key>