WCAG 2.2 AA compliance for ActivityHistoryList

Start the audit with Flutter's built-in Semantics debugger: wrap the widget in `SemanticsDebugger(child: ActivityHistoryList(...))` during a local debug run and screenshot the semantic tree — this reveals unlabelled nodes and incorrect roles faster than manual review. For live region announcements, call `SemanticsService.announce('More activities loaded', TextDirection.ltr)` inside the state listener that detects a transition from isLoading=true to isLoading=false when items.length increases. Guard with a mounted check if called from an async context. For touch target compliance, wrap the retry button in a `SizedBox(width: 44, height: 44)` and centre the visual button inside it using `Align` — this satisfies the touch target without inflating the visual size.

For contrast verification, use the design token colour names and calculate ratios against the surface token: if the design system uses CSS-style token naming, a simple Node script can verify ratios programmatically. The proxy audit badge (from task-003) should already be handled — confirm its semantics were addressed before signing off on this task.

Accessibility-focused widget tests: (1) use `tester.getSemantics()` on the retry button and assert its label is non-empty and size ≥44x44pt; (2) assert SemanticsService.announce is called after a simulated page-2 load using a spy/mock on the semantics service or by checking the semantics tree for the announcement node; (3) use `flutter test --tags=a11y` tag to mark these tests for optional CI exclusion in fast builds but inclusion in nightly runs. Additionally, document in the PR description the result of a manual VoiceOver walkthrough covering: list navigation, empty state, loading state, and error state.

Colour contrast ratios must be measured using the design token values — add a comment in the styles or token file documenting the measured ratios for type label and meta text colours.