feat: sparklines and inline charts for column aggregations

[mpryor]

Summary

Add visual sparklines or inline bar charts to the aggregation view (a) for numeric columns, giving an at-a-glance distribution overview.

Problem

The current aggregation view shows raw numbers (count, sum, avg, min, max). A visual representation would make patterns immediately obvious — skewed distributions, outliers, and trends.

Features

• Inline bar chart or sparkline next to numeric aggregation values
• Histogram view for value distribution within a column
• Optional sparkline column that can be toggled on for any numeric column
• Works with the existing a aggregation keybinding

Technical Considerations

• Use Unicode block characters (▁▂▃▄▅▆▇█) for sparklines
• Should respect the current theme's colors
• Performance: compute lazily, cache results

Related

• Inspired by lnav's bar charts in DB view
• feat: auto-detect column types for type-aware sorting and aggregation #53 (column type detection — needed to identify numeric columns)