Role management and reordering UI

## Summary
Implement role management and reordering with behavior-first parity to Discord for a single guild.

## Scope
- Create, edit, delete, and reorder roles.
- Manage role metadata such as name, color, display behavior, mentionability, and server-level permissions.
- Reflect role order consistently in permission resolution and member presentation.
- Prevent destructive actions that would break baseline server access.

## Acceptance Criteria
- [ ] Authorized users can create, edit, delete, and reorder roles in the UI.
- [ ] Role ordering affects member display and permission precedence consistently.
- [ ] The default everyone role is protected from invalid destructive operations.
- [ ] Users receive clear feedback when a role change would reduce or expand access.

## Operational Notes
- Permission math must stay aligned with Discord-style precedence because later overwrite work depends on it.
- Self-hosted admins need safe defaults that reduce accidental lockout.