feat(ui): Complete Sprint 3500.0004.0002 - UI Components + Visualization
Sprint 3500.0004.0002 - 8/8 tasks completed:
T1: ProofLedgerViewComponent - Merkle tree visualization, DSSE signatures
T2: UnknownsQueueComponent - HOT/WARM/COLD bands, bulk actions
T3: ReachabilityExplainWidget - Canvas call graph, zoom/pan, export
T4: ScoreComparisonComponent - Side-by-side, timeline, VEX impact
T5: ProofReplayDashboardComponent - Progress tracking, drift detection
T6: API services - score.client.ts, replay.client.ts with mock/HTTP
T7: Accessibility - FocusTrap, LiveRegion, KeyNav directives (WCAG 2.1 AA)
T8: Component tests - Full test suites for all components
All components use Angular v17 signals, OnPush change detection, and
injection tokens for API abstraction.
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