feat: Implement Supabase authentication, account management UI, and entitlement services.

frontend/lib/supabase/client.ts

@@ -0,0 +1,29 @@
+import { createBrowserClient } from "@supabase/ssr";
+import type { SupabaseClient } from "@supabase/supabase-js";
+
+let cachedClient: SupabaseClient | null = null;
+
+function readSupabasePublicEnv() {
+  const url = process.env.NEXT_PUBLIC_SUPABASE_URL?.trim();
+  const anonKey = process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY?.trim();
+  return { anonKey, url };
+}
+
+export function hasSupabasePublicEnv() {
+  const { anonKey, url } = readSupabasePublicEnv();
+  return Boolean(url && anonKey);
+}
+
+export function getSupabaseBrowserClient(): SupabaseClient {
+  if (cachedClient) {
+    return cachedClient;
+  }
+
+  const { anonKey, url } = readSupabasePublicEnv();
+  if (!url || !anonKey) {
+    throw new Error("Supabase public env is not configured");
+  }
+
+  cachedClient = createBrowserClient(url, anonKey);
+  return cachedClient;
+}