chore: scaffold Next.js 15 + Supabase clients + vitest

lib/supabase/client.ts

@@ -0,0 +1,9 @@
+// lib/supabase/client.ts
+import { createBrowserClient } from '@supabase/ssr'
+
+export function createClient() {
+  return createBrowserClient(
+    process.env.NEXT_PUBLIC_SUPABASE_URL!,
+    process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!,
+  )
+}