APDU list: the selected row gets a blue tint in dark mode too

- the selection used --bg-input (#334155, a neutral slate) in dark mode, which
  sat right next to the GET RESPONSE pair rows' grey tint
  (--pair-row = rgba(148,163,184,0.12)) and was easy to mistake for them; the
  light theme already had its own blue (#dbeafe) through a
  [data-theme="light"] override
- both themes now set a --selected-bg variable (dark #1e3a8a = blue-900 — the
  palette counterpart of the light blue-100 — light #dbeafe unchanged) and a
  single `.apdu-entry.selected` rule uses it, so the override is gone
- Node test pins the variable in both themes and the single rule
- SW cache simtrace-analyser-v90 (cosmetic, no version bump)

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simtrace-analyser-v89';
+const CACHE = 'simtrace-analyser-v90';
 
 const PRECACHE = [
     'index.html',