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/ui/table/Table.tsx

@@ -14,7 +14,11 @@ import './Table.css';
 
 export interface TableColumn<T> {
   key: string;
-  header: string;
+  // `ComponentChildren`, not `string` — a plain string still satisfies
+  // this and renders identically, but a caller that wants a clickable
+  // sortable header (the issue-report page's own column-header buttons)
+  // can pass real markup instead of forking a second table primitive.
+  header: ComponentChildren;
   render: (row: T) => ComponentChildren;
 }