🟡 MEDIUM: Extract business logic from RegistrationView

[arkavo-com]

Problem

RegistrationView.swift (800 lines) mixes UI code with business logic.

Business Logic in View

1. Form validation - Should be in validator service
2. Screen name availability checking - Should be in service
3. Network calls - Should be in repository
4. Debouncing logic - Should be utility
5. Animation timing - Acceptable in view

Impact

• Cannot unit test validation logic
• Business rules scattered in UI code
• Difficult to reuse validation elsewhere

Proposed Architecture

Registration Feature
├── RegistrationView (~400 lines)
│   └── Pure UI, delegates to ViewModel
├── RegistrationViewModel (~200 lines)
│   └── UI state, form state
├── RegistrationValidator (~100 lines)
│   └── Validation rules, error messages
└── ScreenNameService (~100 lines)
    └── Availability checking, debouncing

Acceptance Criteria

• View reduced to <400 lines
• Validation rules testable without UI
• Screen name checking in dedicated service
• All business logic unit tested