Add .env.example file with API URL configuration

.env.example

@@ -0,0 +1 @@
+VITE_API_URL=http://localhost:8000/api/v1/

src/vite-env.d.ts

@@ -1 +1,9 @@
 /// <reference types="vite/client" />
+
+interface ImportMetaEnv {
+  readonly VITE_API_URL: string;
+}
+
+interface ImportMeta {
+  readonly env: ImportMetaEnv;
+}