feat: add Supabase email auth with signup/login gate

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/authClient.ts

@@ -0,0 +1,14 @@
+/// <reference types="node" />
+import { createClient } from '@supabase/supabase-js';
+
+const url = process.env.SUPABASE_URL || '';
+const key = process.env.SUPABASE_ANON_KEY || '';
+
+export const supabaseAuth = createClient(url, key, {
+  auth: {
+    autoRefreshToken: true,
+    persistSession: true,
+    detectSessionInUrl: true,
+    storageKey: 'craze-auth-session',
+  },
+});