fix: remove Content-Type header from logout request (no body to send)

src/admin/context/AuthContext.tsx

@@ -222,7 +222,7 @@ export function AuthProvider({ children }: { children: ReactNode }) {
       const token = getAccessTokenFn()
       await fetch(`${API_BASE}/logout`, {
         method: 'POST',
-        headers: { 'Content-Type': 'application/json', ...(token && { Authorization: `Bearer ${token}` }) },
+        headers: { ...(token && { Authorization: `Bearer ${token}` }) },
         credentials: 'include',
       })
     } catch { /* ignore */ } finally {