feat: introduce backend url environment variable

ref: N25B-352

src/vite-env.d.ts

@@ -0,0 +1,11 @@
+/// <reference types="vite/client" />
+
+interface ImportMetaEnv {
+  readonly VITE_API_BASE_URL?: string;
+}
+
+interface ImportMeta {
+  readonly env: ImportMetaEnv;
+}
+
+declare const __VITE_API_BASE_URL__: string | undefined;