This fixes the "Authorization header required for API calls" error during
vendor onboarding after signup.
Changes:
- Generate JWT access token on signup completion
- Set vendor_token cookie for page navigation
- Return access_token in signup response for localStorage
- Store vendor_token in localStorage after signup completion
- Make clearTokens() context-aware to prevent cross-portal interference
- Fix vendor logout to not clear admin/customer tokens
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
