Auto-detect window corner radius; anti-alias the mask

Measure the picked window's real corner radius from the capture itself
(the crop's corner pixels are the desktop background; app content starts
where the color departs), correct for arc anti-aliasing, and fall back to
10pt when ambiguous. The clip mask is supersampled 3x for smooth edges.

💘 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>1.8.4</string>
+    <string>1.8.5</string>
     <key>CFBundleVersion</key>
-    <string>84</string>
+    <string>85</string>
     <key>LSUIElement</key>
     <true/>
     <key>NSHighResolutionCapable</key>