chore(pos): cache epos-print.js in the PWA app shell

public/pos/sw.js

@@ -1,5 +1,5 @@
 // Service worker — cache app shell, network-first for HTML + theme.js, cache-first for other static.
-const CACHE = "pos-v15";
+const CACHE = "pos-v16";
 const APP_SHELL = [
   './',
   './index.html',
@@ -9,6 +9,7 @@ const APP_SHELL = [
   './cashup.html',
   './pos-config.js',
   './pos-app.js',
+  './epos-print.js',
   './theme.js',
   './manifest.json',
   // Font Awesome 6 Free (solid) — bundled so the till still renders icons offline.