`UTable`: no way to set arbitrary attributes on `<th>` (`meta.class.th` / `meta.style.th` exist, no attribute equivalent) — blocks `aria-sort`

Description

UTable renders sortable column headers but never emits aria-sort on the <th> element. A sortable
column is announced by screen readers as a plain column header with a button inside it, so the current
sort column and direction are not conveyed. aria-sort is the attribute WAI-ARIA defines for exactly
this (ascending / descending / none on the sorted <th>, and it must be present in the
server-rendered payload, not written after hydration).

There is currently no supported way to add it from userland.

What exists today

Table.vue resolves two per-column <th> hooks off columnDef.meta:

<th
  :data-pinned="header.column.getIsPinned()"
  :scope="header.colSpan > 1 ? 'colgroup' : 'col'"
  data-slot="th"
  :class="ui.th({ class: [props.ui?.th, resolveValue(header.column.columnDef.meta?.class?.th, header)] })"
  :style="[getColumnStyles(header.column), resolveValue(header.column.columnDef.meta?.style?.th, header)]"
>

So meta.class.th and meta.style.th are both supported and both receive the header context, which is
exactly what an aria-sort value needs (header.column.getCanSort(), header.column.getIsSorted()).

What is missing

There is no meta.attrs.th (or any other seam) that reaches the <th> element. Concretely:

• the #<column>-header slot renders inside the <th>, so it cannot set an attribute on it;
• props.ui.th is class-only;
• :ui / app.config.ui.table.slots.th are class-only;
• passing attrs through columnDef.meta is silently dropped.

The same gap applies to <td>, <tr>, and the footer <th>, but the header case is the one with a
concrete accessibility consequence.

Reproduction

1. npx nuxi init + @nuxt/ui@4.10.0
2. Render a UTable with sorting enabled on at least one column.
3. Inspect the emitted <thead>: the sortable <th> carries data-pinned, scope, data-slot, class
   and style, but no aria-sort, in any sort state.
4. Try to add it: there is no meta.attrs.th, and the header slot cannot reach the <th>.

Proposed fix

Either of:

A. Emit aria-sort natively (preferred — it is unambiguously correct for a sortable column):

:aria-sort="header.column.getCanSort()
  ? (header.column.getIsSorted() === 'asc'
    ? 'ascending'
    : header.column.getIsSorted() === 'desc' ? 'descending' : 'none')
  : undefined"

B. Add a generic attribute hook mirroring the two that already exist, resolved the same way:

v-bind="resolveValue(header.column.columnDef.meta?.attrs?.th, header)"

(B) also unblocks aria-describedby, abbr, and per-column test hooks without another API each time.

Workaround in use

A build-time vite transform that rewrites the vendored Table.vue and appends the :aria-sort binding
after the :scope anchor. It is pinned to @nuxt/ui@4.10.0 exactly, because it depends on library
internals and a minor bump would move the anchor. It throws at build time when the anchor disappears.
We would rather delete it.

Start in Table.vue, where the existing meta.class.th and meta.style.th hooks are resolved on each header cell. Compare the native aria-sort and generic meta.attrs.th proposals, then verify the chosen approach on the sortable-column reproduction and confirm the attribute is present in the server-rendered thead for each sort state.