Add sortable columns to all data tables

[antarr]

Summary

• Click any column header to sort ascending/descending
• Sort indicators (arrows) show current sort direction
• Works on all 5 data tables: Slow Queries, Query Stats, Tables, Duplicate Indexes, Unused Indexes
• Numeric columns sort numerically, text columns sort alphabetically
• Generic makeSortable() function — no per-table configuration needed

Test plan

• Click column headers on each table to verify sorting
• Verify numeric columns (rows, times, sizes) sort numerically not lexically
• Verify sort arrows appear and toggle direction
• Verify dark theme sort header hover state