XDNS finalmask: Support resolvers (client) and domains (server)

Treat the xdns mask type as a multi-value setting and update forms accordingly. Inbound/outbound UdpMask models now return arrays for xdns (inbound: settings.domains, outbound: settings.resolvers) using Array.isArray checks. UI templates were split so 'header-dns' still uses a single domain string, while 'xdns' renders a tags-style <a-select> for multiple entries (domains/resolvers). Conditionals were made explicit (mask.type === ...) instead of using includes(). Changed files: web/assets/js/model/inbound.js, web/assets/js/model/outbound.js, web/html/form/outbound.html, web/html/form/stream/stream_finalmask.html.

web/assets/js/model/inbound.js

@@ -1073,8 +1073,9 @@ class UdpMask extends XrayCommonClass {
             case 'mkcp-aes128gcm':
                 return { password: settings.password || '' };
             case 'header-dns':
-            case 'xdns':
                 return { domain: settings.domain || '' };
+            case 'xdns':
+                return { domains: Array.isArray(settings.domains) ? settings.domains : [] };
             case 'xicmp':
                 return { ip: settings.ip || '', id: settings.id ?? 0 };
             case 'mkcp-original':