feat(admin): live redis kill-switch on tunnel actions, sortable columns + CSV export + bulk actions, Node 24 LTS

WS1: pin all Docker stages to node:24.16.0-alpine; add engines node>=20.
WS2: lib/redis.ts gains TTL-backed redisSet, redisDel, setTunnelActive (writes tunnel:active:<sub>=1/0 EX 30, TUNNEL_ACTIVE_TTL override, no-op without REDIS_URL); wired into tunnel active/delete/reassign routes.
WS3: sortable columns, CSV export routes (token excluded), and bulk actions (self-account guard) across users/tunnels/audit admin tables.

app/api/admin/audit/route.ts

@@ -16,6 +16,8 @@ export async function GET(req: NextRequest) {
   const perPage = parsePerPageParam(url.searchParams.get('perPage'), 50, 100);
   const action = url.searchParams.get('action') ?? '';
   const targetType = url.searchParams.get('target_type') ?? '';
+  const sort = url.searchParams.get('sort');
+  const order = url.searchParams.get('order');
 
   try {
     const { entries, total } = await getAuditList({
@@ -23,6 +25,8 @@ export async function GET(req: NextRequest) {
       perPage,
       action,
       targetType,
+      sort,
+      order,
     });
     return jsonNoStore({ entries, total, page, perPage });
   } catch (e) {