Add window detection capture with rounded corners

Hovering during selection now highlights the window under the cursor;
clicking captures it with a rounded-corner alpha mask matching macOS
window chrome. Dragging still switches to manual marquee selection.

💘 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>1.4.3</string>
+    <string>1.5.0</string>
     <key>CFBundleVersion</key>
-    <string>43</string>
+    <string>50</string>
     <key>LSUIElement</key>
     <true/>
     <key>NSHighResolutionCapable</key>