Improve chat text contrast and readability in dark mode

Problem

Several text elements in Windows Companion chat have insufficient contrast in dark mode and are difficult or impossible to read. This may be an accessibility issue for users with low vision or reduced contrast sensitivity.

In the attached example, the following elements appear especially faint:

• The Assistant is thinking... status
• Message timestamp and model metadata
• Model, agent, and mode selector text
• Secondary text and controls near the message composer

Some controls look disabled even when they are available because their foreground color is too close to the dark background.

Screenshot

Expected behavior

• All essential text and interactive controls remain clearly readable in dark mode.
• Text and UI components meet applicable WCAG 2.2 contrast requirements, including at least 4.5:1 for normal text and 3:1 for large text and meaningful UI components.
• Enabled and disabled states are visually distinguishable without making enabled controls appear unavailable.
• Contrast remains sufficient across hover, focus, selected, loading, and disabled states.

Acceptance criteria

• Audit dark-mode foreground and background color combinations in the native chat surface.
• Correct the contrast of status text, metadata, selectors, composer text, and interactive icons.
• Add or update automated accessibility and theme tests for affected components.
• Verify keyboard focus indicators and screen-reader labels remain available after the visual changes.

Start by locating the native Windows Companion chat surface and its dark-mode foreground and background styles for status text, metadata, selectors, composer controls, and icons. Audit the affected states against the stated WCAG contrast ratios, then run or add automated accessibility and theme tests covering focus, hover, selected, loading, and disabled states.