Colour filters: invert, greyscale, high contrast, custom tints

[Maxaubert]

Colour filters for low vision: invert colours, greyscale, high contrast, and custom tints (dimmed, yellow-on-black and similar), with a hotkey to toggle.

• Transform engine: MagSetFullscreenColorEffect (the colour matrix Windows Magnifier uses), done by DWM, near-zero cost per frame
• Render engine: the same 5x5 matrix in the pixel shader
• Settings: preset picker plus a toggle hotkey; applies while zoomed, with an option for 1x too
• Mind the HDR path in the render engine (HDR: magnified view doesn't match the desktop's SDR content brightness #160) and that the matrix is DWM-global while the context lives

Suggested 2026-09-29 in the product-ideas review.

[Maxaubert]

Shipped in 0.14.0 via #300.