Adds client-side sorting to /supplier-invoices: all seven columns get the
same accessible SortableHeader as /invoices, backed by a pure comparator
(Swedish collation, nulls last, displayed-value semantics, stable
invoice_date/id tie-break). The click cycle is tri-state (asc, desc, back
to the API default of due date ascending) per the verifikat-list
precedent, since this list has a meaningful default order to return to.
The detail-pager list context follows the sorted order.
Claude-Session: https://claude.ai/code/session_01DZSVsZqbx8vDnC2SXunNaR
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>