fix: remove remaining /api/ double-prefix from template literal API calls

Previous fix missed backtick template strings. Fixed 7 more api.*()
calls in appointments, deadlines, settings, and einstellungen pages.

frontend/src/components/settings/CalDAVSettings.tsx

@@ -68,7 +68,7 @@ export function CalDAVSettings({ tenant }: { tenant: Tenant }) {
         typeof window !== "undefined"
           ? localStorage.getItem("kanzlai_tenant_id")
           : null;
-      return api.put<Tenant>(`/api/tenants/${tenantId}/settings`, {
+      return api.put<Tenant>(`/tenants/${tenantId}/settings`, {
         caldav: cfg,
       });
     },