feat: implement Supabase authentication with Google OAuth

Add Supabase client, middleware, and auth pages; update header for auth state.

Co-authored-by: ASOwnerYT <[email protected]>

lib/supabase/client.ts

@@ -0,0 +1,8 @@
+import { createBrowserClient } from '@supabase/ssr'
+
+export function createClient() {
+  return createBrowserClient(
+    process.env.NEXT_PUBLIC_SUPABASE_URL!,
+    process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!,
+  )
+}