Release 0.2.1: PRView Rules-of-Hooks fix (React #310 blank page)

PRView.jsx declared its threadsByKind useMemo after the early-return
guard for the loading state. First mount: pr is null, early return
fires, 14 hooks called. Second render: pr populated, execution
reaches the useMemo, 15 hooks — React #310, page goes blank.

Move the useMemo above the early returns and null-safe the
pr?.threads access so the hook count stays stable across renders.

Pre-existing bug in the post-Contribute-rewrite PR view; surfaced
in production by 0.2.0's graduation merge race fix enabling the
workflow that opens this code path. Patch per §20.2 — no operator
action required beyond rebuilding the frontend and restarting.

CHANGELOG.md

@@ -23,6 +23,28 @@ skip versions are the composition of each intervening adjacent
 release's steps in order — no A-to-B path is pre-computed beyond
 that.
 
+## 0.2.1 — 2026-05-26
+
+**Patch — no operator action required.** Rebuild the frontend and
+restart per the routine deploy steps; no `.env` changes, no schema
+changes, no behavior changes a deployment would notice in steady
+state.
+
+### Fixed
+
+- **PR view blank page (React #310).** `frontend/src/components/PRView.jsx`
+  declared its `threadsByKind` `useMemo` *after* the early-return
+  guard for the loading state (`if (!pr) return …`). On first mount
+  `pr` was null so the early return fired and 14 hooks were called;
+  on the second render `pr` was populated and execution reached the
+  `useMemo`, calling 15 hooks — violating the Rules of Hooks and
+  unmounting the page subtree (blank screen). The `useMemo` is now
+  declared above the early returns with optional-chaining on `pr`,
+  keeping the hook count stable between the loading and loaded
+  renders. Pre-existing bug in the post-Contribute-rewrite PR view;
+  surfaced in production by 0.2.0's graduation merge race fix
+  enabling the workflow that opens this code path.
+
 ## 0.2.0 — 2026-05-26
 
 **Breaking config change.** The frontend now requires