Summary of Working HDR Pixel Reading with ScreenCaptureKit

I have a working HDR pixel reader. Key discoveries and solutions:

**1. Pixel Format - CRITICAL:**
```swift
config.pixelFormat = kCVPixelFormatType_64RGBAHalf // Float16 RGBA for HDR
```

**2. Reading Float16 Values:**
```swift
// Each pixel is 8 bytes: 4 channels × 2 bytes (Float16)
let pixelOffset = y * bytesPerRow + x * 8
let pixelPointer = baseAddress.advanced(by: pixelOffset)
let rgba16 = pixelPointer.bindMemory(to: UInt16.self, capacity: 4)

// Convert UInt16 bit patterns to Float16, then to Float
let r = Float(Float16(bitPattern: rgba16[0]))
let g = Float(Float16(bitPattern: rgba16[1]))
let b = Float(Float16(bitPattern: rgba16[2]))
```

**3. Cursor Avoidance - THE KEY FIX:**
The cursor itself is white (1.0, 1.0, 1.0) and gets captured! Offset sampling by at least 10 pixels from cursor position:
```swift
let bufferX = Int(round((mouseX - screenFrame.minX) * scaleX)) - 20 + 4  // 10 logical pixels left
let bufferY = Int(round((screenFrame.maxY - mouseY) * scaleY)) - 20 - 2  // 10 logical pixels up
```
(The -20+4 and -20-2 account for the 2x backing scale on Retina displays)

**4. Coordinate Conversion:**
Use `round()` instead of `Int()` truncation for accurate pixel alignment.

**5. EDR Headroom Check:**
```swift
let edrHeadroom = nsScreen.maximumExtendedDynamicRangeColorComponentValue
// Values can exceed this on XDR displays with HDR content
```

**Previous Problem:** We were reading the cursor itself, which is always white, capping values at 1.0. The offset fixes this.

Can you help me apply these fixes to my magnification app?
