Update app icon to Avigilon Alta logo, remove Test Connection button, rename proxy buttons

- Replace app icon (assets/icon.png) with Avigilon Alta "A" logo
- Add Windows .ico version of the icon
- Remove Test Connection button from API Connection section
- Rename Start/Stop Cookie Proxy buttons to Start/Stop Proxy
- Add .claude/ and nul to .gitignore

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

package.json

@@ -37,7 +37,9 @@
   "devDependencies": {
     "electron": "^28.0.0",
     "electron-builder": "^26.4.0",
-    "electron-packager": "^17.1.2"
+    "electron-packager": "^17.1.2",
+    "png-to-ico": "^3.0.1",
+    "sharp": "^0.34.5"
   },
   "dependencies": {
     "axios": "^1.6.0",