feat(ui): add /dash route, shared nav, project dashboard with /v1/projects API

Restructure routes: / and /dash show a project overview dashboard,
/activity hosts the existing timeline, /cv remains. Shared Layout
component provides consistent nav header and footer across all routes.

New /v1/projects endpoint aggregates per-repo activity stats (commits,
issues, PRs, date range) from existing event data via SQL. Dashboard
ranks projects by weighted recency + volume score and renders a card
grid.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/App.tsx

@@ -5,20 +5,20 @@ import 'rc-slider/assets/index.css';
 import 'react-vertical-timeline-component/style.min.css';
 import './App.css';
 
+import { Layout } from './components/Layout';
+import { DashPage } from './pages/DashPage';
 import { TimelineHome } from './pages/TimelineHome';
 import { CvPage } from './pages/CvPage';
 
 export default function App() {
   return (
-    <>
-      <Routes>
-        <Route path="/" element={<TimelineHome />} />
+    <Routes>
+      <Route element={<Layout />}>
+        <Route index element={<DashPage />} />
+        <Route path="/dash" element={<DashPage />} />
+        <Route path="/activity" element={<TimelineHome />} />
         <Route path="/cv" element={<CvPage />} />
-      </Routes>
-      <footer className="site-footer">
-        no cookies are set or read by this site, which is why no consent banner
-        is shown.
-      </footer>
-    </>
+      </Route>
+    </Routes>
   );
 }