swarm-ui: add the custom issue-report page

New /issues route: a sortable, filterable table over open issues across
every repo that has one -- repo picker (default: no filter, every repo
combined), hide-blocked toggle, and a label multi-select, consuming
swarm-controller's GET /api/repos + GET /api/issue-report / GET
/api/repos/{org}/{repo}/issue-report (see hyperhive#3831 for the row
shape). blocked and depended_on_by_count arrive pre-resolved per row --
this page does no dependency-graph walking of its own, just sort/filter
over what it's given. Default sort is depended_on_by_count descending,
matching mara's framing of the report's headline ordering.

Widened Table's TableColumn.header from string to ComponentChildren so
a column can carry a real clickable sort-toggle button instead of
forking a second table primitive for this one page.

frontend/packages/swarm-ui/src/shell/Shell.tsx

@@ -48,6 +48,7 @@ const NAV_ITEMS: { href: string; label: string; accent: string }[] = [
   { href: '/', label: 'hives', accent: 'var(--purple)' },
   { href: '/agents', label: 'agents', accent: 'var(--green)' },
   { href: '/jobs', label: 'jobs', accent: 'var(--pink)' },
+  { href: '/issues', label: 'issues', accent: 'var(--yellow)' },
   { href: '/components', label: 'components', accent: 'var(--blue)' },
 ];