ui: shorten the preset list's keyset column header to "KIc/KID — counter"

The full "Keysets (number: ...)" context repeated the column's topic; the
header now reads just the byte pair and the counter.  The header text node
also carried a literal \u2014 escape (it only rendered correctly once
translatePage() rewrote it) - now a real em dash.

sw cache simple-v367.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simple-v366';
+const CACHE = 'simple-v367';
 const URLS = [
   'index.html',
   'help.html',