Implement Timeline component

[superposition]

Description

Build the historical playback timeline.

Tasks

• Create timeline/Timeline.tsx
• Implement progress bar with full width
• Add event markers at significant blocks
• Show event names on hover
• Implement drag-to-seek functionality
• Display current position (block number, date)
• Highlight current event severity with color

Acceptance Criteria

• Timeline shows full historical range
• Events are clearly marked
• Seeking is smooth and responsive

Labels

web-app, frontend, timeline