fix(finalmask): hop client UDP through the udphop mask

xray-core 26.9.9 dropped finalmask.quicParams.udpHop for the client-only
"udphop" UDP mask {mode, interval, remoteIPs, remotePorts}. The panel kept
writing the old key, so hysteria/xhttp outbounds and JSON-subscription
clients silently stopped hopping ports.

An inbound keeps quicParams.udpHop: it is panel metadata advertised as the
link's mport, and a udphop mask on a listener fails with "udphop: client
only". The conversion (maskcompat.UpgradeLegacyUDPHop, intervalRemote mode)
runs only where a client config is produced:

- UDPHopClientMaskFix seeder over hosts, sub-JSON finalmask, cached
  outbound-subscription outbounds and template outbounds (never inbounds);
- GetXrayConfig heals template outbounds at build time;
- the JSON subscription upgrades each generated client stream;
- the Go and frontend link importers upgrade a legacy fm= param.

The finalmask editor gains a side prop: the client side lifts the dead key
on mount and offers a udphop mask editor (also for xhttp's HTTP/3 dial);
the inbound side keeps the UDP Hop switch, labelled as advertised.

frontend/src/lib/xray/outbound-link-parser.ts

@@ -1,5 +1,6 @@
 import { Base64 } from '@/utils';
 
+import { upgradeLegacyUdpHop } from './udphop-mask';
 import { upgradeLegacyXdnsMasks } from './xdns-mask';
 
 // Focused share-link parser for the OutboundFormModal's link-import
@@ -272,8 +273,8 @@ const kcpHeaderTypeToMask: Record<string, string> = {
 };
 
 // The inbound link emits the entire finalmask object as a JSON-encoded
-// `fm` query param. Decode and attach to streamSettings so udpHop /
-// quicParams / tcp+udp masks round-trip on outbound import.
+// `fm` query param. Decode and attach to streamSettings so quicParams and the
+// tcp+udp masks round-trip on outbound import; a legacy udpHop becomes the mask.
 function applyFinalMaskParam(stream: Raw, params: URLSearchParams): void {
   const fm = params.get('fm');
   if (fm) {
@@ -282,7 +283,7 @@ function applyFinalMaskParam(stream: Raw, params: URLSearchParams): void {
       if (parsed && typeof parsed === 'object') {
         sanitizeFinalMaskQuicParams(parsed);
         if (Array.isArray(parsed.udp)) parsed.udp = upgradeLegacyXdnsMasks(parsed.udp).next;
-        stream.finalmask = parsed;
+        stream.finalmask = upgradeLegacyUdpHop(parsed).next;
       }
     } catch {
       // malformed fm — leave streamSettings.finalmask absent