fix: keep env var validation, only skip in test mode

Throw on missing VITE_SUPABASE_URL/ANON_KEY except when MODE=test
(set automatically by vitest).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: francofrizzo

src/lib/supabaseClient.ts

@@ -1,6 +1,12 @@
 import { createClient } from "@supabase/supabase-js";
 
-const supabaseUrl = import.meta.env.VITE_SUPABASE_URL ?? "http://localhost";
-const supabaseAnonKey = import.meta.env.VITE_SUPABASE_ANON_KEY ?? "dummy";
+const supabaseUrl = import.meta.env.VITE_SUPABASE_URL;
+const supabaseAnonKey = import.meta.env.VITE_SUPABASE_ANON_KEY;
 
-export const supabase = createClient(supabaseUrl, supabaseAnonKey);
+if (!supabaseUrl || !supabaseAnonKey) {
+  if (import.meta.env.MODE !== "test") {
+    throw new Error("Missing VITE_SUPABASE_URL or VITE_SUPABASE_ANON_KEY");
+  }
+}
+
+export const supabase = createClient(supabaseUrl ?? "http://localhost", supabaseAnonKey ?? "dummy");