Table columns: sizing & persistence

[BradEstey]

Column widths

• Columns now divide the panel instead of overflowing.
• Removed the 16px scrollbar gutter down the right of the table.
• A dragged width is remembered per column set.
• Showing, hiding or reordering a column clears every stored width, so the list goes back to its computed tracks rather than re-applying an old answer.
• A ResizeObserver drops the layout the kit's resizer freezes inline, so the tracks refit when the panel or the column set changes.
• Use @toolpath/ui Menu components.
• Use @toolpath/ui Toggle component for toggling inches to mm.

Guardrails

• AGENTS.md gains Reach for @toolpath/ui first, and kit-usage.test.ts budgets createPortal to the one file that genuinely needs it.