Let system dialogs take clicks during capture; hint Esc on the overlay

The event tap consumes every click while selecting, which made permission
prompts unclickable when they appeared mid-capture. Clicks now pass
through when a system dialog (SecurityAgent / System Settings) is
frontmost, and the overlay shows a visible Esc hint as an escape hatch.

💘 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>1.8.6</string>
+    <string>1.8.7</string>
     <key>CFBundleVersion</key>
-    <string>86</string>
+    <string>87</string>
     <key>LSUIElement</key>
     <true/>
     <key>NSHighResolutionCapable</key>