Fix hyperion-project#1921: replace per-frame SCScreenshotManager with persistent SCStream

Previously capture15() called getShareableContentWithCompletionHandler on
every single frame grab (10-60 times/second), causing WindowServer to spike
in CPU usage and occasional frame-rate drops on macOS Tahoe.

Replace with a persistent SCStream (started once in setDisplayIndex):
- getShareableContentWithCompletionHandler is called only once at setup
- HyperionStreamOutput (SCStreamOutput delegate) receives frames on a
  high-priority dispatch queue and stores the latest CVPixelBuffer
- grabFrame() reads directly from the CVPixelBuffer — no CIImage/CIContext
  overhead, no per-frame system enumeration
- Stream pixel format kCVPixelFormatType_32BGRA maps directly to BGR32,
  eliminating an extra copy/conversion step
- Falls back to single-shot screenshot if the stream fails to start or
  no frame has been delivered yet

Additional fixes in the same file:
- Fix missing braces in setupDisplay() that caused early return even when
  CGRequestScreenCaptureAccess() succeeded
- Fix CGDisplayModeRef leak in capture15() (missing CGDisplayModeRelease)
- Fix CGColorSpaceRef leak in capture15() (CGColorSpaceCreateDeviceRGB
  result was never released)
- Reduce queueDepth from 5 to 3 for lower latency

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tpmodding

include/grabber/osx/OsxFrameGrabber.h

@@ -17,7 +17,6 @@ class OsxFrameGrabber : public Grabber
 	/// Construct a OsxFrameGrabber that will capture snapshots with specified dimensions.
 	///
 	/// @param[in] display The index of the display to capture
-
 	///
 	OsxFrameGrabber(int display=kCGDirectMainDisplay);
 	~OsxFrameGrabber() override;
@@ -58,4 +57,19 @@ class OsxFrameGrabber : public Grabber
 
 	/// Reference to the captured display
 	CGDirectDisplayID _display;
+
+#if defined(SDK_15_AVAILABLE)
+	/// SCStream* stored as opaque pointer to keep ObjC out of this C++ header
+	void* _stream;
+	/// HyperionStreamOutput* stored as opaque pointer
+	void* _streamOutput;
+
+	/// Start a persistent SCStream for the given display.
+	/// Calls getShareableContentWithCompletionHandler only once (at setup).
+	/// @return true on success
+	bool startStream(CGDirectDisplayID displayID);
+
+	/// Stop and release the active SCStream.
+	void stopStream();
+#endif
 };