feat: column auto-fit (double-click divider + context menu) (#511)

* feat: add column auto-fit (double-click divider + context menu)

- Implement tableView(_:sizeToFitWidthOfColumn:) delegate for native
  double-click-on-column-divider auto-fit (matches Finder/Numbers)
- Add "Size to Fit" to column header right-click menu
- Add "Size All Columns to Fit" to column header right-click menu
- All three reuse existing calculateOptimalColumnWidth() logic
- Works in both table data tab and SQL query results tab

* fix: use uncapped width calculation for user-initiated auto-fit

Author: datlechin