PhoenixKit V08 Migration: Username Support

This migration adds username functionality to the user system, allowing users to have unique usernames in addition to their email addresses.

Changes

Username System

• Adds username field to phoenix_kit_users table
• Creates unique constraint on username field
• Migrates existing users to have default usernames based on email
• Provides username validation and generation logic

New Features

• Username Field: Optional unique username for each user
• Email-based Generation: Automatically generates usernames from email addresses
• Uniqueness Handling: Handles duplicate usernames with incremental suffixes
• Backwards Compatibility: Existing functionality remains unchanged

PostgreSQL Support

• Supports PostgreSQL prefix for schema isolation
• Optimized indexes for username lookups
• Safe migration of existing user data