Improve dashboard contribution calendar timeline

[ventura-oss]

Summary

• Change the contribution calendar summary from calendar-week activity to rolling last 7 days vs prior 7 days
• Make the heatmap larger and move compact KPI tiles to the right edge of the heatmap
• Add continuous log-scaled heatmap coloring so higher-count days remain visually distinct

Screenshots

Before

After

Testing

• npm run build

[ventura-oss]

Updated this PR to the month-based hourly contribution timeline.

• Month buttons run left-to-right.
• The heatmap shows a dynamic trailing history window that fills the available width without horizontal scrolling.
• Footer now includes selected range comparison plus selected month vs prior month counts.
• Month switching avoids per-cell MUI tooltips and reuses cached hourly aggregation.

Latest screenshot:

[ventura-oss]

Closing this in favor of a fresh PR with the final dashboard calendar timeline screenshots/context.