feat: add ZEROPS_TOKEN environment variable authentication

[fxck]

Summary

• Add support for ZEROPS_TOKEN environment variable to bypass zcli login
• Auto-login behavior: automatically saves token and region data to storage
• Uses identical region fetching logic as login command for consistency
• Handles missing region data gracefully with default region fallback

Usage

# Set token and get automatically logged in
ZEROPS_TOKEN=your_token_here zcli project list

# Subsequent commands work without env var
zcli service list
zcli deploy

Benefits

• Developer Experience: One-command authentication setup
• CI/CD Ready: Perfect for automation and scripts
• Consistent Behavior: Same validation and storage as zcli login
• Performance: Subsequent commands use cached region data

Implementation Details

• Reuses existing region resolution logic from login command
• Auto-saves token and region data like zcli login does
• Maintains full backward compatibility with existing authentication
• No breaking changes to guest commands or stored login sessions

Test plan

• Build and test CLI with environment token
• Verify authentication persists after initial env token usage
• Confirm auto-login saves token and region data to storage
• Ensure existing login-based authentication continues to work
• Test fallback behavior for missing region data
• Verify guest commands remain unaffected

[tikinang]

Some changes are unnecessary, overly complicated. Simpler implementation here: #228