a11y: contrast audit — metrics, diff, and component tree views (WCAG 1.4.3)

[jamilagibson]

Context

The connection status indicator and primary UI have been audited for contrast. The metrics displays, snapshot diff view, and component tree have not been fully audited against WCAG 1.4.3 minimums.

Compliance target: WCAG 2.1 Level AA — 4.5:1 for normal text, 3:1 for large text and UI components.

Scope

• CommitMetrics table (header text, cell text, border colors)
• LagMetrics list
• FirstRenderMetric display
• SnapshotDiff view (added/removed/changed color coding must not rely on color alone — WCAG 1.4.1)
• ComponentTree node labels and expand/collapse indicators

Acceptance criteria

• Full axe DevTools scan with zero color contrast violations
• Diff view color coding supplemented with text labels or icons (not color alone)
• Results documented in ACCESSIBILITY.md

Tools

• axe DevTools browser extension
• Colour Contrast Analyser (for spot checks)