Make Stop Capture button red and prominent

- Add --danger/--danger-hover CSS variables (dark + light themes)
- .stop button now uses red background + white text with brighter hover
  (was muted gray, easy to miss)
- Bump 1.22.3, SW cache v34->v35

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simtrace-analyser-v34';
+const CACHE = 'simtrace-analyser-v35';
 
 const PRECACHE = [
     'index.html',