flatten app to repo root and update docker deployment for single-stack runtime

app/api/portfolio/summary/route.ts

@@ -0,0 +1,8 @@
+import { buildPortfolioSummary } from '@/lib/server/portfolio';
+import { getStoreSnapshot } from '@/lib/server/store';
+
+export async function GET() {
+  const snapshot = await getStoreSnapshot();
+  const summary = buildPortfolioSummary(snapshot.holdings);
+  return Response.json({ summary });
+}