fix(table): make the column resize handle keyboard and touch accessible

[ndlabdev]

Summary

The column resize handle was a bare span carrying only onmousedown, with no role, no tabindex and no key handler. I measured it before changing anything, with a mouse drag as the control case that proves the probe works:

Table  resize handle : {"role":null,"tabindex":null,"ariaLabel":null,"ariaValueNow":null}
focusable            : false

column width          : 150
after 3 arrow presses : 150   (unchanged)
after an 80px drag    : 230   (changed, so the mouse path works)

Tabbing from a button placed immediately above the table jumped straight past the whole table into the next component, so the table offered no keyboard stop for resizing at all.

The same wiring broke pointer input other than a mouse, because the drag listened for mousemove and mouseup on document:

after a touch pointer drag : 150   (unchanged)
after touchstart           : 150   (unchanged)
handle has touch-none      : true

The touch-none class suggests touch was intended. As it stood the class blocked scrolling that began on the handle without offering anything back.

Closes #226

Type of change

• 🐛 Bug fix
• ✨ New feature / component
• 📖 Documentation
• ♻️ Refactor / chore
• ⚠️ Breaking change

Changes

• The handle is now a focusable separator with aria-orientation, aria-valuenow, aria-valuemin, aria-valuemax and aria-valuetext, so assistive technology can announce the current width.
• Arrow keys resize by 16px, or 64px while shift is held. Home goes to minWidth and End to maxWidth, and End is inert on a column that sets no maximum.
• The drag moves onto usePointerDrag, the hook ColorPicker and Resizable already use, so touch and pen work instead of a mouse alone. This also removes the manual document listeners.
• Width clamping now lives in one place, shared by the pointer and keyboard paths.
• resizing is a plain local instead of $state, since nothing reactive reads it.

Accessibility notes

The svelte-ignore for static element interactions is gone, because the element is genuinely interactive now. One ignore remains, for the noninteractive tabindex rule, which reads a separator as passive and does not account for one carrying aria-valuenow. That is the same false positive Resizable already suppresses, so the two controls are now consistent.

Checklist

• Linked the related issue (Closes #226)
• pnpm check passes (0 errors, 0 warnings)
• pnpm lint passes
• pnpm test passes
• Added or updated tests for the change
• Updated CHANGELOG.md under [Unreleased]
• Followed component conventions (no comments outside *.types.ts, Material 3 design tokens)

Notes

Verified on a throwaway page driven through a real browser, with one column bounded only at the bottom and another bounded at both ends:

Name (min 80, no max)
  200 -> Arrow 216 (+16) -> Shift+Arrow 280 (+64) -> Home 80 -> End 80 (inert, correct)

Role (min 100, max 260)
  160 -> End 260 (hits the max) -> Arrow 260 (does not exceed it)

touch pointer drag of 70px : 80 -> 150

Seven regression tests cover the separator attributes, focusability, arrow resizing, the shift step, clamping at the minimum, a touch pointer drag, and that a column without resizable renders no handle. The probe page is deleted.