Add vite env typings

Author: Yann Leflour

ui-sketcher-webview/src/vite-env.d.ts

@@ -1 +1,10 @@
 /// <reference types="vite/client" />
+
+interface ImportMetaEnv {
+  readonly VITE_OPENAI_API_KEY: string;
+  // more env variables...
+}
+
+interface ImportMeta {
+  readonly env: ImportMetaEnv;
+}