feat: add CalDAV settings UI and team management pages (Phase 3P)

Backend: PUT /api/tenants/{id}/settings endpoint for updating tenant
settings (JSONB merge). Frontend: /einstellungen page with CalDAV
config (URL, credentials, calendar path, sync toggle, interval),
manual sync button, live sync status display. /einstellungen/team
page with member list, invite-by-email, role management.

frontend/src/app/(app)/einstellungen/page.tsx

@@ -0,0 +1,116 @@
+"use client";
+
+import { useQuery } from "@tanstack/react-query";
+import { Settings, Calendar, Users } from "lucide-react";
+import Link from "next/link";
+import { api } from "@/lib/api";
+import type { Tenant } from "@/lib/types";
+import { CalDAVSettings } from "@/components/settings/CalDAVSettings";
+import { SkeletonCard } from "@/components/ui/Skeleton";
+import { EmptyState } from "@/components/ui/EmptyState";
+
+export default function EinstellungenPage() {
+  const tenantId =
+    typeof window !== "undefined"
+      ? localStorage.getItem("kanzlai_tenant_id")
+      : null;
+
+  const {
+    data: tenant,
+    isLoading,
+    error,
+    refetch,
+  } = useQuery({
+    queryKey: ["tenant-current", tenantId],
+    queryFn: () => api.get<Tenant>(`/api/tenants/${tenantId}`),
+    enabled: !!tenantId,
+  });
+
+  return (
+    <div className="mx-auto max-w-3xl space-y-6 p-4 sm:p-6">
+      <div className="flex items-center justify-between">
+        <h1 className="text-lg font-semibold text-neutral-900">
+          Einstellungen
+        </h1>
+        <Link
+          href="/einstellungen/team"
+          className="inline-flex items-center gap-1.5 rounded-md border border-neutral-200 bg-white px-3 py-1.5 text-sm font-medium text-neutral-700 hover:bg-neutral-50"
+        >
+          <Users className="h-3.5 w-3.5" />
+          Team verwalten
+        </Link>
+      </div>
+
+      {/* Tenant Info */}
+      {isLoading ? (
+        <>
+          <SkeletonCard />
+          <SkeletonCard />
+        </>
+      ) : error ? (
+        <EmptyState
+          icon={Settings}
+          title="Fehler beim Laden"
+          description="Einstellungen konnten nicht geladen werden."
+          action={
+            <button
+              onClick={() => refetch()}
+              className="rounded-md bg-neutral-900 px-3 py-1.5 text-sm font-medium text-white hover:bg-neutral-800"
+            >
+              Erneut versuchen
+            </button>
+          }
+        />
+      ) : tenant ? (
+        <>
+          {/* Kanzlei Info */}
+          <section className="rounded-xl border border-neutral-200 bg-white p-5">
+            <div className="flex items-center gap-2.5 border-b border-neutral-100 pb-3">
+              <Settings className="h-4 w-4 text-neutral-500" />
+              <h2 className="text-sm font-semibold text-neutral-900">
+                Kanzlei
+              </h2>
+            </div>
+            <div className="mt-4 grid gap-3 sm:grid-cols-2">
+              <div>
+                <p className="text-xs text-neutral-500">Name</p>
+                <p className="text-sm font-medium text-neutral-900">
+                  {tenant.name}
+                </p>
+              </div>
+              <div>
+                <p className="text-xs text-neutral-500">Slug</p>
+                <p className="text-sm font-medium text-neutral-900">
+                  {tenant.slug}
+                </p>
+              </div>
+              <div>
+                <p className="text-xs text-neutral-500">Erstellt am</p>
+                <p className="text-sm text-neutral-700">
+                  {new Date(tenant.created_at).toLocaleDateString("de-DE", {
+                    day: "2-digit",
+                    month: "2-digit",
+                    year: "numeric",
+                  })}
+                </p>
+              </div>
+            </div>
+          </section>
+
+          {/* CalDAV Settings */}
+          <section className="rounded-xl border border-neutral-200 bg-white p-5">
+            <div className="flex items-center gap-2.5 border-b border-neutral-100 pb-3">
+              <Calendar className="h-4 w-4 text-neutral-500" />
+              <h2 className="text-sm font-semibold text-neutral-900">
+                CalDAV-Synchronisierung
+              </h2>
+            </div>
+            <div className="mt-4">
+              <CalDAVSettings tenant={tenant} />
+            </div>
+          </section>
+        </>
+      ) : null}
+    </div>
+  );
+}

frontend/src/app/(app)/einstellungen/team/page.tsx

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+"use client";
+
+import Link from "next/link";
+import { ArrowLeft, Users } from "lucide-react";
+import { TeamSettings } from "@/components/settings/TeamSettings";
+
+export default function TeamPage() {
+  return (
+    <div className="mx-auto max-w-3xl space-y-6 p-4 sm:p-6">
+      <div className="flex items-center gap-3">
+        <Link
+          href="/einstellungen"
+          className="rounded-md p-1.5 text-neutral-400 hover:bg-neutral-100 hover:text-neutral-600"
+        >
+          <ArrowLeft className="h-4 w-4" />
+        </Link>
+        <div className="flex items-center gap-2.5">
+          <Users className="h-4 w-4 text-neutral-500" />
+          <h1 className="text-lg font-semibold text-neutral-900">
+            Team verwalten
+          </h1>
+        </div>
+      </div>
+
+      <section className="rounded-xl border border-neutral-200 bg-white p-5">
+        <div className="border-b border-neutral-100 pb-3">
+          <h2 className="text-sm font-semibold text-neutral-900">
+            Mitglieder
+          </h2>
+          <p className="mt-0.5 text-xs text-neutral-500">
+            Benutzer einladen und Rollen verwalten
+          </p>
+        </div>
+        <div className="mt-4">
+          <TeamSettings />
+        </div>
+      </section>
+    </div>
+  );
+}