feat: Add Registry Developer Account Registration

[roncodes]

Overview

This PR adds the flb register command to enable users to create Registry Developer Accounts directly from the CLI.

Changes

New Command: flb register

Adds a new registration command with the following features:

• Interactive prompts for username, email, password, and optional full name
• Input validation:
  • Username: min 3 characters, alphanumeric with hyphens/underscores only
  • Email: valid email format required
  • Password: min 8 characters required
• API integration: Calls POST /~registry/v1/developer-account/register
• Error handling: Displays validation errors from API responses
• User guidance: Provides clear next steps after successful registration

Usage

# Interactive mode
flb register

# With options
flb register -u myusername -e user@example.com -p mypassword -n "John Doe"

Output Example

✓ Account created successfully!
✓ Please check your email to verify your account.

✓ Once verified, you can login with: flb login -u myusername

Benefits

✅ Seamless onboarding for self-hosted users
✅ No need to visit web interface for registration
✅ Consistent CLI experience
✅ Clear validation and error messages

Testing

• Test interactive registration flow
• Test registration with command-line options
• Test validation error handling
• Test API error handling
• Test success message and guidance

Related

This PR works in conjunction with the registry-bridge PR #27 that implements the backend support for Registry Developer Accounts.