feat: icon extraction from .exe files

- electron/main.ts: extractExeIcon() via app.getFileIcon(), saves PNG to
  userData/icons/{md5}.png; IPC icon:extract; scanner:import now auto-extracts
- electron/preload.ts: expose extractIcon()
- AdminPanel: Scan button next to image field — extracts icon from current exe
  (shows animated pulse while loading, error if no exe selected or extraction fails)
- GameCard: isExtractedIcon() detects icons/ path; renders centered 64x64 icon
  on gradient background instead of stretched cover

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "club-launcher",
-  "version": "1.3.0",
+  "version": "1.3.1",
   "description": "Game launcher for computer club",
   "author": "houseassassin",
   "main": "out/main/main.js",