fix: handle empty BASE_URL in buildUrl to prevent Invalid URL error

When VITE_API_BASE_URL is unset, BASE_URL defaults to '', which causes
new URL(path, '') to throw TypeError: Invalid URL. Fall back to
location.origin (browser/jsdom) or 'http://localhost' (SSR).

src/api/client.ts

@@ -28,7 +28,8 @@ interface RequestOptions {
 }
 
 function buildUrl(path: string, params?: ListParams): string {
-  const url = new URL(path, BASE_URL)
+  const base = BASE_URL || (typeof location !== 'undefined' ? location.origin : 'http://localhost')
+  const url = new URL(path, base)
   if (params) {
     for (const [key, value] of Object.entries(params)) {
       if (value !== undefined && value !== null && value !== '') {