Add freehand drawing and fix residual capture pixelation

The screenshot window now supports toggling a pen to draw annotations
that are flattened into copied and saved images. Captures are also
cropped with a pixel-exact CGImage.cropping instead of a CGContext
redraw, removing residual blur on retina displays.

💘 Generated with Crush

Assisted-by: Crush:deepseek-v4-flash-0731

Sources/Kapture/CaptureController.swift

@@ -134,15 +134,11 @@ final class ScreenCapture {
         // display's frame (e.g. secondary monitor coordinate quirks).
         let safeRect = pxRect.intersection(CGRect(x: 0, y: 0, width: CGFloat(image.width), height: CGFloat(image.height)))
         guard safeRect.width >= 1, safeRect.height >= 1 else { return nil }
-        guard let cropCtx = CGContext(
-            data: nil, width: Int(safeRect.width), height: Int(safeRect.height),
-            bitsPerComponent: 8, bytesPerRow: 0,
-            space: CGColorSpaceCreateDeviceRGB(),
-            bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue
-        ) else { return nil }
-        cropCtx.interpolationQuality = .high
-        cropCtx.draw(image, in: CGRect(x: -safeRect.minX, y: -safeRect.minY, width: CGFloat(image.width), height: CGFloat(image.height)))
-        return cropCtx.makeImage()
+        // Use a pixel-exact subimage crop instead of redrawing through a
+        // CGContext, which resamples and loses quality on retina captures.
+        let rounded = safeRect.integral
+        guard rounded.width >= 1, rounded.height >= 1 else { return nil }
+        return image.cropping(to: rounded)
     }
 
     @available(macOS 14.0, *)