feat: UI for server/channel creation, settings link, role management backend

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

web/src/App.tsx

@@ -6,6 +6,7 @@ import { UserSettings } from './components/UserSettings.tsx';
 import { BotManager } from './components/BotManager.tsx';
 import { CommandManager } from './components/CommandManager.tsx';
 import { RoleManager } from './components/RoleManager.tsx';
+import { JoinServer } from './components/JoinServer.tsx';
 import { useAuthStore } from './stores/auth.ts';
 
 function ProtectedRoute({ children }: { children: React.ReactNode }) {
@@ -90,6 +91,14 @@ function App() {
             </ProtectedRoute>
           }
         />
+        <Route
+          path="/invites/:code"
+          element={
+            <ProtectedRoute>
+              <JoinServer />
+            </ProtectedRoute>
+          }
+        />
         <Route
           path="/"
           element={