Summary

Adds a new is_oauth_registration_enabled setting so administrators can allow OAuth-based self-registration while keeping general (password-based) registration disabled. Closes #8042.

Re-submitted after addressing Copilot review (null-safe default in mount()).

Changes

• Migration: Adds is_oauth_registration_enabled boolean column to instance_settings (default: false)
• OauthController: OAuth callback now allows new user creation when either is_registration_enabled OR is_oauth_registration_enabled is true
• Advanced Settings (Livewire): Added property with null-safe default (?? false), validation rule, mount/save logic
• Blade view: Added checkbox toggle with helper text in admin Advanced settings

How it works

Existing OAuth users can always log in regardless — these settings only affect new account creation.

/claim #8042