fix: group toast icon, left-click spell suggestions, scroll no-yank (0.1.12/batch66)

1. Group message toast had no icon: the generated group icon is a data: URL, but
   the 0.1.11 handler only used ALREADY-cached icons and skipped it. data: URLs
   are synchronous — use them immediately, so every group toast shows an icon.
2. Spell suggestions on a LEFT click: clicking a red-squiggled word in the message
   box now pops the native suggestions menu (renderer asks the shell to synthesize
   a right-click at that point → real dictionary suggestions). No right-click.
3. Scroll felt "stuck" because an incoming message yanked you to the bottom even
   when you'd scrolled up to read history (worse now that bg messages arrive live).
   appendBubble now keeps your position unless you were at the bottom / it's your
   own message, and surfaces the "jump to latest" control instead.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

desktop/package.json

@@ -1,6 +1,6 @@
 {
   "name": "biz-connect-desktop",
-  "version": "0.1.11",
+  "version": "0.1.12",
   "description": "Biz Connect technician desktop client — loads the Connect web UI with native screen capture",
   "author": {
     "name": "BizGaze",