Switch frame loop from dispatch timer to CADisplayLink at 30fps

Replace the high-priority dispatch timer with CADisplayLink for frame
updates, reducing target framerate from 60 to 30 fps. This simplifies
the frame loop implementation while providing better system integration.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

screendump/FrameUpdater.m

@@ -7,7 +7,6 @@
 	NSOperationQueue *_q;
 	BOOL _updatingFrames;
 	CADisplayLink *_displayLink;
-	dispatch_source_t _timer;
 
 	// Shared from ScreenDumpVNC
 	IOSurfaceRef _screenSurface;
@@ -142,11 +141,6 @@
 -(void)stopFrameLoop {
 	_updatingFrames = NO;
 
-	if (_timer) {
-		dispatch_source_cancel(_timer);
-		_timer = nil;
-	}
-
 	if (_displayLink) {
 		dispatch_async(dispatch_get_main_queue(), ^(void){
 			[_displayLink invalidate];
@@ -159,23 +153,11 @@
 	[self stopFrameLoop];
 	_updatingFrames = YES;
 
-	// Use high-priority dispatch timer instead of CADisplayLink
-	// CADisplayLink may be throttled for daemon processes
-	dispatch_queue_attr_t attr = dispatch_queue_attr_make_with_qos_class(
-		DISPATCH_QUEUE_SERIAL, QOS_CLASS_USER_INTERACTIVE, 0);
-	dispatch_queue_t timerQueue = dispatch_queue_create("com.mousen.screendump.frametimer", attr);
-
-	_timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, DISPATCH_TIMER_STRICT, timerQueue);
-
-	// 60 FPS = ~16.67ms interval
-	uint64_t interval = NSEC_PER_SEC / 60;
-	dispatch_source_set_timer(_timer, dispatch_time(DISPATCH_TIME_NOW, 0), interval, 0);
-
-	dispatch_source_set_event_handler(_timer, ^{
-		[self _updateFrame];
+	dispatch_async(dispatch_get_main_queue(), ^{
+		_displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(_updateFrame)];
+		_displayLink.preferredFramesPerSecond = 30;
+		[_displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
 	});
-
-	dispatch_resume(_timer);
 }
 
 -(void)dealloc {