Add KeyboardTester.click monitor color/banding test

[nasirazizawan009]

Adds a relevant tool for designers picking color schemes:

Monitor Color & Banding Test (https://keyboardtester.click/color-test.php) - Free browser tool that displays solid R/G/B/W/K panels and 1024-step linear gradients to check whether your monitor is rendering smooth color transitions or showing banding (which would distort how your color schemes appear). Includes 6-bit vs 8-bit vs 10-bit panel discussion.

Open source: https://github.com/nasirazizawan009/keyboardtester-click

[nasirazizawan009]

Hi, just checking whether this monitor color/banding test is a useful fit for the list. The tool is meant to help designers verify whether a display is showing smooth gradients and solid colors correctly before judging palettes or visual work.

I can shorten the wording if the entry needs to be more compact.