fix(auth): Improve OAuth credential detection and startup warning

- Enhanced getClaudeAuthIndicators() to return detailed check information
  including file paths checked and specific error details for debugging
- Added debug logging to server startup credential detection for easier
  troubleshooting in Docker environments
- Show paths that were checked in the warning message to help users debug
  mount issues
- Added support for CLAUDE_CODE_OAUTH_TOKEN environment variable
- Return authType in verify-claude-auth response to distinguish between
  OAuth and CLI authentication methods
- Updated UI to show specific success messages for Claude Code subscription
  vs generic CLI auth
- Added Docker troubleshooting tips to sandbox risk dialog
- Added comprehensive unit tests for OAuth credential detection scenarios

Closes #721

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/ui/src/lib/electron.ts

@@ -1442,6 +1442,7 @@ interface SetupAPI {
   verifyClaudeAuth: (authMethod?: 'cli' | 'api_key') => Promise<{
     success: boolean;
     authenticated: boolean;
+    authType?: 'oauth' | 'api_key' | 'cli';
     error?: string;
   }>;
   getGhStatus?: () => Promise<{