Add an event navigator with filters and graph seeking

[raphant]

Problem

Long sessions are difficult to inspect from a flat timeline.
Users cannot quickly find errors, permission waits, one tool type, or one agent and jump the graph to that event.

Proposed change

Add an event navigator that filters by event type, agent, tool, and text.
Selecting a result should seek Review mode and highlight the related graph node.

Acceptance criteria

• Users can filter errors, permissions, tools, agents, and messages.
• Search matches visible event labels and transcript text.
• Selecting a result seeks Review mode to the event time.
• The related agent or tool node receives visible focus.
• Previous-problem and next-problem controls work from the keyboard.

Source

• web/components/agent-visualizer/timeline-panel.tsx renders the current timeline.
• web/components/agent-visualizer/control-bar.tsx owns Review mode seeking.