Add grip dots visual indicator to splitter bar

- ::after pseudo-element with radial-gradient dot pattern
- Dots darken on hover/active for contrast against accent background
- Bump 1.22.14, SW cache v45->v46

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simtrace-analyser-v45';
+const CACHE = 'simtrace-analyser-v46';
 
 const PRECACHE = [
     'index.html',