Scrollbars: one 12px style for every pane

- the APDU list's 12px rule is folded into the global scrollbar style, so
  the side panel, APDU detail pane, dialogs (file-diff body), session
  lists/grid and the hex views' horizontal bars all use the same 12px bar
  with a 6px rounded thumb — no per-element overrides remain to drift,
  and the horizontal bars get an explicit height instead of the browser
  default
- Node test pins the global rule (12px width/height, 6px thumb radius) and
  the absence of per-element overrides; 527 Python + 55 Node tests
- SW cache simtrace-analyser-v75 (cosmetic, no version bump)

frontend/index.html

@@ -120,10 +120,6 @@ body { font: 14px/1.5 system-ui, sans-serif; background: var(--bg); color: var(-
 
 /* APDU list */
 .apdu-list { flex: 1 1 0; min-height: 0; overflow-y: auto; padding: 8px; }
-.apdu-list::-webkit-scrollbar,
-.side-panel::-webkit-scrollbar { width: 12px; }
-.apdu-list::-webkit-scrollbar-thumb,
-.side-panel::-webkit-scrollbar-thumb { border-radius: 6px; }
 .apdu-entry { display: flex; gap: 12px; padding: 3px 12px; border-bottom: 1px solid var(--bg-panel); cursor: pointer; align-items: baseline; }
 .apdu-entry.apdu-pair { background: var(--pair-row); }
 .apdu-entry:hover { background: var(--bg-panel); }
@@ -319,10 +315,11 @@ body { font: 14px/1.5 system-ui, sans-serif; background: var(--bg); color: var(-
 .comprion-error { font-size: 12px; line-height: 1.45; color: var(--error); margin-top: 8px; }
 .comprion-error:empty { display: none; }
 
-/* Scrollbar */
-::-webkit-scrollbar { width: 6px; }
+/* Scrollbar — one style for every pane (APDU list, side panel, APDU detail,
+   dialogs, session lists, the hex views' horizontal bars) */
+::-webkit-scrollbar { width: 12px; height: 12px; }
 ::-webkit-scrollbar-track { background: var(--scrollbar-track); }
-::-webkit-scrollbar-thumb { background: var(--scrollbar-thumb); border-radius: 3px; }
+::-webkit-scrollbar-thumb { background: var(--scrollbar-thumb); border-radius: 6px; }
 </style>
 </head>
 <body>