Frontend:
- Settings link in header next to logout
- [+] button to create server (name + optional icon)
- [#] button to join server via invite code
- [+] button to create channel (name, type, category)
- Server name shown instead of UUID in channel list header
- /invites/:code route wired for JoinServer component
Backend:
- Wire role CRUD + member-role assignment routes (MANAGE_SERVER gated)
- Seed @everyone default role on server creation