refactor: organize desktop vs. mobile into separate folders

js/desktop/vite.env.ts

@@ -0,0 +1,13 @@
+// Shared Vite `define` block that injects the build-time __APP_ENV__ constant
+// consumed by src/config/env.ts. Sourced from process.env.APP_ENV (default 'dev').
+
+const raw = process.env.APP_ENV ?? "dev";
+if (raw !== "dev" && raw !== "prod") {
+  throw new Error(`APP_ENV must be "dev" or "prod", got: ${raw}`);
+}
+
+export const appEnv = raw;
+
+export const defineEnv = {
+  __APP_ENV__: JSON.stringify(appEnv),
+};