swarm ui: a pull requests card on the reports tab

The reports tab gets a "pull requests" card under the issue report. It lists
the open PRs of every repo, or of one picked in a repo select, with the
columns a reviewer or merger filters on: author, labels, requested
reviewers, base branch, WIP (the forge's draft flag), approvals against the
base branch's protection rule, has all approvals, conflicts, protected base
and CI. Every column sorts, the small-set columns filter by picking values,
and the browser keeps the filters and the repo. No filter applies at first.

swarm-controller resolves each row so the page makes no calls of its own:
GET /api/pr-report and GET /api/repos/{org}/{repo}/pr-report. The required
approvals come from the first matching branch protection rule (an
unprotected base asks for none); an approval counts when it is the
reviewer's latest decision, on the current head, neither stale nor
dismissed and official.

A free-text table cell gets a minimum width, so a table with many columns
scrolls sideways instead of wrapping a title to a word a line.

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

@@ -31,6 +31,9 @@
    not a short discrete label) rather than open-ended growth that drags
    the whole table wider — caps the column and wraps within it instead. */
 .ui-table-prose {
+  /* A table with many columns squeezes free text to a word a line;
+     the table scrolls sideways instead. */
+  min-width: 14em;
   max-width: 32em;
   white-space: normal;
   word-break: break-word;