fix: resolve __dirname error by forcing Node.js runtime on all server routes

- Add serverExternalPackages for @supabase/ssr in next.config.ts
- Add export const runtime = 'nodejs' to all pages/routes using Supabase
- Replace createAdminClient to use @supabase/supabase-js directly (no SSR)
- Prevents @supabase/ssr from running in Edge runtime on Vercel

https://claude.ai/code/session_01H2aRGDaKgarPvhay2HxN6Y

app/(protected)/dashboard/page.tsx

@@ -4,6 +4,8 @@ import ProgressBar from "@/components/dashboard/ProgressBar";
 import ModuleCard from "@/components/dashboard/ModuleCard";
 import type { Module, UserProgress, Profile } from "@/types/database.types";
 
+export const runtime = "nodejs";
+
 export default async function DashboardPage() {
   const supabase = await createClient();