build: add staging/prod scripts and env type definitions

update the default build script to use production mode
define TypeScript types for all supported Vite environment variables

src/env.d.ts

@@ -1,5 +1,18 @@
 /// <reference types="vite/client" />
 
+interface ImportMetaEnv {
+  readonly VITE_APP_ENV: "development" | "staging" | "production";
+  readonly VITE_API_BASE_URL: string;
+  readonly VITE_API_TIMEOUT_MS?: string;
+  readonly VITE_SOCKET_BASE_URL?: string;
+  readonly VITE_CLIENT_ID?: string;
+  readonly VITE_TOKEN?: string;
+}
+
+interface ImportMeta {
+  readonly env: ImportMetaEnv;
+}
+
 declare module "*.vue" {
   import type { DefineComponent } from "vue";