…n accessibility

- Import and expose filesSortingStore via setup() replacing dead local data() properties
- Fix ariaSortForMode('basename') -> ariaSortForMode('name') mismatch with button mode prop
- Return 'none' instead of null for sortable-but-inactive columns (required by ARIA spec)
- Add scope="col" to all <th> elements so screen readers associate headers with columns

Signed-off-by: Vitor Mattos <[email protected]>

Cover isAscending computed property, --active CSS class presence,
and toggleSortBy delegation for active/inactive column states

Signed-off-by: Vitor Mattos <[email protected]>

…eHeader

Verify ascending/descending/none/null return values and corresponding
aria-sort DOM attribute for sortable and non-sortable columns

Signed-off-by: Vitor Mattos <[email protected]>

Upload PDF, add signer, send request, navigate to Files list sorted by
Created at descending, rename to unique name, assert Ready to sign status,
delete via actions menu and confirm row disappears

Signed-off-by: Vitor Mattos <[email protected]>

Upload PDF, place a visible signature element, save, navigate away and
return to verify the element persists, then delete it and confirm it is
removed after a second round-trip

Signed-off-by: Vitor Mattos <[email protected]>