A11y: audit muted text contrast on dark theme

[sbrants]

Summary

WaveTrace uses a dark UI. Secondary text (--muted and similar tokens in src/styles.css) has not had a formal contrast pass against WCAG 2.2 AA.

Task

1. Audit muted labels, hints, and table secondary text on Dashboard, History, and Settings.
2. Adjust CSS custom properties (or specific rules) so normal-sized text meets 4.5:1 contrast on the default background where feasible.
3. Note any exceptions (e.g. disabled states) in a short comment in docs/accessibility.md Phase D or in the PR description.

No screen-reader or chart work required — CSS and visual verification only.

Why

Small, self-contained improvement from docs/accessibility.md Phase D. npm run lint should still pass.

References

• src/styles.css — theme tokens
• docs/accessibility.md — Phase D
• CONTRIBUTING.md