Improve dashboard contribution calendar interactions

[ventura-oss]

Summary

• replace the native heatmap cell title with a styled tooltip showing date, hour window, and contribution count
• hide heatmap cells for hours that have not fully concluded yet
• improve selected month button contrast without the connector highlight bleed
• reduce month-switch rendering cost by avoiding MUI wrappers for heatmap cells and caching built calendar results per month/range/current hour

Before / After

Before

After

Testing

• npm run build