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.css

@@ -53,6 +53,50 @@ a.hot-pink {
   color: #1565c0;
 }
 
+.site-header h1 {
+  font-size: 1.75rem;
+}
+
+.site-header nav a {
+  color: #ecf0f1;
+  opacity: 0.7;
+}
+
+.site-header nav a:hover {
+  color: #ff4081;
+  opacity: 1;
+  text-decoration: none;
+}
+
+.site-header nav a.active {
+  color: #ff4081;
+  opacity: 1;
+}
+
+.nav-divider {
+  opacity: 0.3;
+}
+
+.project-card {
+  background: rgba(255, 255, 255, 0.05);
+  border: 1px solid rgba(255, 255, 255, 0.1);
+  border-radius: 6px;
+  height: 100%;
+}
+
+.project-card h5 {
+  font-size: 0.9rem;
+}
+
+.project-card a {
+  color: #ff4081;
+}
+
+.project-card .text-muted {
+  color: rgba(236, 240, 241, 0.5) !important;
+  font-size: 0.7rem;
+}
+
 .site-footer {
   margin-top: 3rem;
   padding: 1rem 0;