bucket-bar: hide scrollbar, soft edge fades, wheel-to-scroll

The horizontal scrollbar on the bucket row was ugly and
inconsistent with the rest of the app's scrollbar-less panels. Hide
it, redirect vertical wheel over the bar to horizontal scroll, and
surface overflow with soft bg-coloured gradients on whichever side
has more content off-screen: right only while anchored at the
start, both in the middle, left only at the end.

Fade overlays live on #bucket-row (parent) as pseudo-elements with
pointer-events:none, rather than mask-image on the bar itself — a
mask would also clip super-bucket popovers that are intentionally
rendered inside #bucket-bar for the collab MutationObserver.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

electron/package.json

@@ -1,6 +1,6 @@
 {
   "name": "hyprcrd",
-  "version": "1.9.6",
+  "version": "1.9.7",
   "description": "hyprcrd — self-hosted card manager",
   "main": "main.js",
   "scripts": {