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

app/api/health/route.ts

@@ -0,0 +1,16 @@
+import { getStoreSnapshot } from '@/lib/server/store';
+
+export async function GET() {
+  const snapshot = await getStoreSnapshot();
+  const queue = snapshot.tasks.reduce<Record<string, number>>((acc, task) => {
+    acc[task.status] = (acc[task.status] ?? 0) + 1;
+    return acc;
+  }, {});
+
+  return Response.json({
+    status: 'ok',
+    version: '3.0.0',
+    timestamp: new Date().toISOString(),
+    queue
+  });
+}