AUTH-004: Organizations - Models and Service

[lbedner]

Priority: High | Estimate: L

Implement Orgs level (Level 3) - backend:

• Organization model (name, slug, plan, is_active, timestamps)
• OrgMembership model (user_id, org_id, role, joined_at)
• OrgService with CRUD operations
• MembershipService for managing org members

Files

• aegis/templates/.../app/models/organization.py (new)
• aegis/templates/.../app/models/org_membership.py (new)
• aegis/templates/.../app/services/auth/org_service.py (new)
• aegis/templates/.../app/services/auth/membership_service.py (new)
• aegis/core/migration_generator.py (org tables spec)

Acceptance Criteria

• Models created with proper relationships
• Services have full CRUD
• Migration generates org + org_membership tables
• Files only generated when auth_level is org