Add login-required user management (admin/user roles, Config->Benutzer)

No self-signup: admins create every account in Config -> Benutzer with a
typed start password; a forced password change gates first use. Session-
cookie auth protects all /api/* routes; /api/users additionally requires
the admin role. See docs/authentication.md.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/frontend/components/Sidebar.tsx

@@ -6,6 +6,7 @@ import { useEffect, useState } from "react";
 import { listProjects } from "../utils/api";
 import type { ProjectDto } from "../types";
 import { ThemeToggle } from "./ThemeToggle";
+import { useAuth } from "./AuthProvider";
 
 // Anchors on the project overview page (/projects/[id]).
 const PROJECT_SECTIONS = [
@@ -30,6 +31,7 @@ interface SidebarProps {
 
 export function Sidebar({ isCollapsed, onToggleCollapsed }: SidebarProps) {
   const pathname = usePathname();
+  const { user, isAdmin, logout } = useAuth();
   const projectMatch = pathname?.match(PROJECT_PATH_PATTERN);
   const activeProjectId = projectMatch ? projectMatch[1] : null;
   const projectSubPath = projectMatch?.[2] ?? "";
@@ -179,8 +181,31 @@ export function Sidebar({ isCollapsed, onToggleCollapsed }: SidebarProps) {
           </>
         )}
       </nav>
+      {isAdmin && (
+        <nav className="sidebar-nav sidebar-nav-bottom">
+          <Link
+            href="/config"
+            className={pathname?.startsWith("/config") ? "sidebar-link active" : "sidebar-link"}
+            title="Config"
+          >
+            <span className="sidebar-icon">⚙</span>
+            <span className="sidebar-label">Config</span>
+          </Link>
+        </nav>
+      )}
       <div className="sidebar-footer">
+        {user && !isCollapsed && (
+          <div className="sidebar-identity" title={`Angemeldet als ${user.name}`}>
+            <span className="sidebar-identity-label">Angemeldet als</span>
+            <span className="sidebar-identity-name">{user.name}</span>
+          </div>
+        )}
         <ThemeToggle />
+        {user && (
+          <button type="button" className="sidebar-logout" onClick={() => void logout()}>
+            {isCollapsed ? "⏻" : "Abmelden"}
+          </button>
+        )}
       </div>
     </aside>
   );