Make the Reservoir artifact table sortable

Page: /reservoir. Source: report-projects-rbac-reservoir-scheduler.md section 3. All <=26.4.0.

The table has no sorter on any column and the order is hard-coded to UPDATED_AT DESC. Expose NAME, TYPE, SIZE, SCANNED_AT, UPDATED_AT ordering through the column headers with UPDATED_AT DESC as the default.

JIRA Issue: FR-3919

Start at the /reservoir page and read section 3 of report-projects-rbac-reservoir-scheduler.md to locate the artifact table and its current ordering. Add header sorting for NAME, TYPE, SIZE, SCANNED_AT, and UPDATED_AT while preserving UPDATED_AT DESC as the default, then verify each column order in the page.

Written by the indexing model from the issue text.