Recording Phase 5: Timeline-Correlated Playback and Diagnostic UX

[mark-e-deyoung]

Context\nUsers/agents need fast navigation from incidents to precise timeline context.\n\n## Scope\nAdd a lightweight timeline viewer in dashboard UX tied to recording markers and operations.\n\n## Requirements\n- Add timeline panel showing markers and correlated operation IDs.\n- Provide jump-to-time affordances for recorded artifacts.\n- Show clear correlation between API operations, marker events, and artifact files.\n\n## Acceptance Criteria\n- E2E covers marker rendering and interaction basics.\n- UX remains usable in both desktop/mobile dashboard modes.\n- Documentation updated with operator workflow examples.