fix(whiteboard): keep the chosen hue visible when the brush is dark

[criticalAY]

Purpose / Description

The whiteboard color picker ignores the color you choose when the current brush is dark: you tap a color on the wheel, press OK, and the brush stays black (or comes back near-black). This makes it impossible to add a custom brush color starting from the default black brush.

The cause is how the picker is built. The wheel only controls hue and saturation; brightness is a separate slider below it. When the picker opens on a dark color, that slider is parked near zero, and the final color is assembled from the slider's
brightness. So no matter where you tap on the wheel, the result assembles back to near-black and the picker looks broken.

Fixes

• Fixes Unable to select custom brush color for whiteboard #21329

Approach

On the first touch of the wheel, if the current color's brightness is near zero (the slider is parked there), snap the brightness slider to full before the tap is handled. This covers pure black and dark non-black seeds like #030000, without affecting normal picking.

How Has This Been Tested?

Pixel 10 and added Robolectric unit tests in ColorPickerDialogTest

Screen_recording_20260702_182437.mp4

Learning (optional, can help others)

Describe the research stage

Links to blog posts, patterns, libraries or addons used to solve this problem

Checklist

Please, go through these checks before submitting the PR.

• You have a descriptive commit message with a short title (first line, max 50 chars).
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner