[UX] Time-lapse map slider — animate 287(g)/detainer spread by year

[wi287g]

A year slider that animates county color changes over time — a powerful accountability and journalism tool.

Tasks

• Add <input type="range"> year slider to toolbar
• On change, re-color county layer based on detainer data for that year
• Add play/pause button to auto-advance slider (setTimeout loop)
• Add a snapshot permalink (?year=2023) so journalists can link to a specific year
• Ensure the slider year state is reflected in chart views too