Feature: Automatic event clustering when multiple events overlap

[thbst16]

Description

When multiple events occur in the same year or time period, they can overlap and become unreadable. The component should support automatic clustering with expand-on-click behavior.

Use Case

In 1960, the AFL was founded with multiple charter teams (Bills, Patriots, Broncos, etc.) and the Cowboys joined the NFL. These events stack on top of each other, making labels difficult to read.

Proposed Solution

• Add clustering prop with options: 'auto' | 'manual' | 'none'
• When clustered, show a count badge (e.g., "+5 events")
• Clicking a cluster expands to show individual events in a popup or stacked view
• Allow clusterThreshold to configure proximity sensitivity

Example API

<Timeline
  data={data}
  clustering="auto"
  clusterThreshold={{ days: 365 }}  // cluster events within 1 year
/>

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Issue generated from user feedback while building an NFL history timeline