swarm-ui: sortable + filterable table columns

hyperhive#4020, mara. TableColumn gets two new optional extractors,
each one the whole signal for its capability (mara: 'why separate
selector and flag?' — dropped the sortable/filterable booleans that
would've said the same thing twice and could disagree with the
extractor's presence):

- sortBy: (row) => string | number — column is click-to-sort iff
  present. Table owns the sort state (one active column, header click
  cycles none -> ascending -> descending), since a rendered cell often
  isn't the sortable value itself (e.g. AgentsPage's status column
  renders a Badge, not a plain string).
- filterValue: (row) => string — column is filterable iff present. A
  text input row under the headers, substring match case-insensitive.

Client-side only, no backend change - every consuming page already
fetches its full row set. Wired into AgentsPage and HivesPage, the two
pages with a real per-row Table. Left IssueReportPage alone (already
has its own purpose-built sort + label/hide-blocked filters, predates
this and covers its own domain better than a generic per-column text
filter would) and JobsPage alone (renders an indented state tree via
JobqGraph, no column table at all despite what my original scoping
comment assumed).

Verified: typecheck + build clean, nix fmt clean, static render of the
actual built CSS confirms the new sort-header + filter-row markup
doesn't break table layout.

frontend/packages/swarm-ui/src/ui/table/Table.css

@@ -35,3 +35,49 @@
   white-space: normal;
   word-break: break-word;
 }
+
+/* Sortable header — the whole header cell is the click target, not a
+   separate icon-only button next to it, same "control lives on the
+   thing it affects" reasoning as `Badge`'s own click-to-toggle shape. */
+.ui-table-sort-button {
+  display: inline-flex;
+  align-items: center;
+  gap: 0.35em;
+  background: none;
+  border: none;
+  padding: 0;
+  margin: 0;
+  font: inherit;
+  font-weight: 600;
+  color: inherit;
+  cursor: pointer;
+}
+.ui-table-sort-button:hover {
+  color: var(--fg);
+}
+.ui-table-sort-glyph {
+  opacity: 0.6;
+  font-size: 0.85em;
+}
+.ui-table-sort-button:hover .ui-table-sort-glyph {
+  opacity: 1;
+}
+
+/* The per-column filter inputs' row — same cell padding as a header row,
+   no bottom border of its own (the header row above already has one). */
+.ui-table-filter-row th {
+  padding-top: 0;
+  padding-bottom: 0.5em;
+  font-weight: 400;
+}
+.ui-table-filter-input {
+  width: 100%;
+  box-sizing: border-box;
+  background: var(--bg);
+  color: var(--fg);
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  padding: 0.25em 0.5em;
+  font: inherit;
+  font-size: 0.9em;
+}