Fix Actions column border: keep td.actions as a table-cell

.actions sets display:inline-flex (correct for a button container), but it was
applied directly to <td class="actions">, pulling the cell out of the table row
box so its bottom border rendered ~1px off from the other columns. Override
td.actions back to display:table-cell and space multiple buttons with a margin
instead of the flex gap.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/assets/style.css

@@ -941,8 +941,17 @@ input[type="radio"] {
 }
 
 td.actions {
+  /* A td must stay display:table-cell - the .actions inline-flex above pulls
+     the cell out of the table's row box, so its bottom border renders ~1px off
+     from the other cells. Keep it a cell; space multiple buttons with a margin
+     instead of the flex gap. */
+  display: table-cell;
+  vertical-align: middle;
   white-space: nowrap;
 }
+td.actions .btn + .btn {
+  margin-left: 0.25rem;
+}
 
 /* ============================================
    DETAIL PAGES (shared styles)