super-buckets: split tab click (activate) from caret click (dropdown)

Clicking the super-bucket tab now activates the last-shown child
directly. Only the caret arrow on the right opens the dropdown popover.
Caret has its own hit area with accent hover highlight.

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

electron/package.json

@@ -1,6 +1,6 @@
 {
   "name": "hyprcrd",
-  "version": "1.2.0",
+  "version": "1.3.0",
   "description": "hyprcrd — self-hosted card manager",
   "main": "main.js",
   "scripts": {