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>

.gitignore

@@ -20,3 +20,9 @@ Desktop.ini
 .vscode/
 *.swp
 *.swo
+
+# Claude Code
+.claude/
+
+# Windows null device artifact
+nul