Slice 3: the PR flow

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/App.jsx

@@ -3,6 +3,7 @@ import { Routes, Route, Link, useNavigate } from 'react-router-dom'
 import { getMe } from './api'
 import Catalog from './components/Catalog.jsx'
 import RFCView from './components/RFCView.jsx'
+import PRView from './components/PRView.jsx'
 import ProposalView from './components/ProposalView.jsx'
 import ProposeModal from './components/ProposeModal.jsx'
 import Landing from './components/Landing.jsx'
@@ -51,6 +52,7 @@ export default function App() {
           <Routes>
             <Route path="/" element={<Welcome viewer={me.user} />} />
             <Route path="/rfc/:slug" element={<RFCView viewer={me.user} />} />
+            <Route path="/rfc/:slug/pr/:prNumber" element={<PRView viewer={me.user} />} />
             <Route path="/proposals/:prNumber" element={<ProposalView viewer={me.user} onChange={() => setCatalogVersion(v => v + 1)} />} />
           </Routes>
         </main>