feat(desktop): Windows taskbar overlay icon for unread badge

Red-dot overlay drawn as raw RGBA (no extra resource bundled).
Shown on Windows when unread count > 0, cleared when 0.
macOS keeps numeric Dock badge; Linux has no cross-DE badge API.

Bumps version 0.10.0 -> 0.10.1.

apps/desktop/src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
   "productName": "ChatApp",
-  "version": "0.10.0",
+  "version": "0.10.1",
   "identifier": "com.meinname.chatapp",
   "build": {
     "beforeDevCommand": "pnpm vite:dev",