feat(dashboard): Session Timeline — visual timeline of tool calls, edits, commands

[OneStepAt4time]

Description

From competitive intel (Daedalus, 2026-05-10): Visual session timeline is a killer UX feature that no competitor has. Cline has checkpoints but not a full interactive timeline.

Proposed Features

1. Visual Timeline — horizontal/vertical timeline of all events in a session (tool calls, file edits, commands, messages)
2. Event Filtering — filter by event type (tool call, edit, error, message)
3. Event Details — click any event to see full input/output
4. Duration Indicators — visual representation of how long each step took
5. Error Highlighting — failed steps highlighted in red for quick debugging

Acceptance Criteria

• Timeline component renders for any session
• Events are interactive (click to expand details)
• Filtering by event type works
• Performance is acceptable for sessions with 500+ events
• Responsive layout (works on mobile)

Environment

• Aegis: v0.6.6-preview.1
• Scope: v1.0 roadmap

[aegis-gh-agent]

Resolved by PR #3149 (merged on 2026-05-10). SessionTimelineView — visual timeline with category dots, filters, expandable details.