CopilotForXcode stuck at Welcome screen, no authentication code on macOS 15.3.1 (Sonoma)

**Describe the bug**
CopilotForXcode is stuck at the "Welcome to Copilot" screen upon launch. No authentication code is displayed and no pop-up or browser window appears for device login or GitHub sign-in.

**Versions**
- Copilot for Xcode: 0.43.0
- Xcode: [unknown]
- macOS: 15.3.1 (24D70)

**Steps to reproduce**
1. Download and install CopilotForXcode 0.43.0 from official DMG.
2. Move CopilotForXcode to the Applications folder.
3. Eject DMG and launch CopilotForXcode from Applications.
4. App opens to "Welcome to Copilot" screen, but does not display a code or prompt for authentication. No additional windows or browser pop-ups appear.
5. Tried restarting Mac, reinstalling app, checking permissions, and verifying internet connection. Issue persists.

**Screenshots**
N/A

**Logs**
No specific logs found. No error message displayed on the welcome screen.

**Additional context**
- Issue persists after restart and full clean reinstall.
- No hidden windows/dialogs detected (checked with Cmd+Tab and Dock).
- CopilotForXcode permissions verified in Privacy & Security > Accessibility & Automation.
- Issue may be related to compatibility with macOS 15.3.1 (Sonoma).