Enrich per-event RST/VCC labels (ATR STARTS / power-up) + decode server-side

- decode_line_event adds human label: RST de-asserted->ATR STARTS,
  VCC applied->VCC ON (power-up); keep canonical event string
- Enable rst/vcc in DB decode dispatch so PWA receives decoded
  (fixes bare RESET/VCC fallback and a latent showDetail crash)
- PWA line_event_label/showDetail render decoded.label
- Bump 1.22.1, SW cache v32->v33; +1 test

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simtrace-analyser-v32';
+const CACHE = 'simtrace-analyser-v33';
 
 const PRECACHE = [
     'index.html',