feat(api): user-scoped activities CRUD with shared auth helper

apps/api/src/lib/require-user.ts

@@ -0,0 +1,8 @@
+import type { Context } from 'hono';
+import { auth } from '../auth';
+
+export async function getSessionUser(c: Context): Promise<{ id: string } | null> {
+  const session = await auth.api.getSession({ headers: c.req.raw.headers });
+  if (!session) return null;
+  return { id: session.user.id };
+}