feat: refine controls and installation dialog

sw.js

@@ -1,5 +1,5 @@
 // Bump VERSION whenever a shell file changes. New versions wait for approval.
-const VERSION = 'v9';
+const VERSION = 'v16';
 const BASE = self.registration.scope;
 const PREFIX = `ascii-pwa-${encodeURIComponent(BASE)}-`;
 const CACHE = `${PREFIX}${VERSION}`;