fix(macos): add NSScreenCaptureUsageDescription and screen-capture entitlement

Without NSScreenCaptureUsageDescription in Info.plist, macOS silently
blocks desktopCapturer.getSources(), breaking window detection on macOS
10.15+. Also adds the com.apple.security.device.screen-capture entitlement
to macos.entitlements alongside the existing camera and audio-input entries.

Fixes #548

electron-builder.json5

@@ -51,6 +51,7 @@
       "NSAudioCaptureUsageDescription": "OpenScreen needs audio capture permission to record system audio.",
       "NSMicrophoneUsageDescription": "OpenScreen needs microphone access to record voice audio.",
       "NSCameraUsageDescription": "OpenScreen needs camera access to record webcam video.",
+      "NSScreenCaptureUsageDescription": "OpenScreen needs screen recording permission to detect and capture windows.",
       "NSCameraUseContinuityCameraDeviceType": true,
       "com.apple.security.device.audio-input": true
     }

macos.entitlements

@@ -21,5 +21,9 @@
     <!-- Camera (webcam capture) -->
     <key>com.apple.security.device.camera</key>
     <true/>
+
+    <!-- Screen recording (required for desktopCapturer.getSources() on macOS 10.15+) -->
+    <key>com.apple.security.device.screen-capture</key>
+    <true/>
 </dict>
 </plist>