fix(links): use configured domain for panel copy/QR links on loopback

The panel's copy/QR share links are built client-side and fell back to window.location.hostname, so reaching the panel over an SSH tunnel (127.0.0.1/localhost) leaked localhost into the links - unlike the backend subscription path, which falls back to the configured Sub/Web Domain (issue #4829).

Expose webDomain/subDomain via /defaultSettings and add preferPublicHost: when the browser host is loopback, prefer the configured Sub Domain (then Web Domain) for share/QR links. An explicit node override or per-inbound listen still wins; a routable browser host is kept as-is.

Closes #4829

frontend/src/pages/inbounds/qr/QrCodeModal.tsx

@@ -9,6 +9,7 @@ import {
   genWireguardConfigs,
   genWireguardLinks,
   isPostQuantumLink,
+  preferPublicHost,
 } from '@/lib/xray/inbound-link';
 import { inboundFromDb, type DbInboundLike } from '@/lib/xray/inbound-from-db';
 import QrPanel from './QrPanel';
@@ -57,7 +58,7 @@ export default function QrCodeModal({
   useEffect(() => {
     if (!open || !dbInbound) return;
     const inbound = inboundFromDb(dbInbound);
-    const fallbackHostname = window.location.hostname;
+    const fallbackHostname = preferPublicHost(window.location.hostname, subSettings?.publicHost ?? '');
     if (inbound.protocol === Protocols.WIREGUARD) {
       const peerRemark = client?.email
         ? `${dbInbound.remark}-${client.email}`