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.

internal/sub/json_service.go

@@ -16,6 +16,7 @@ import (
 	"github.com/mhsanaei/3x-ui/v3/internal/database/model"
 	"github.com/mhsanaei/3x-ui/v3/internal/logger"
 	"github.com/mhsanaei/3x-ui/v3/internal/util/json_util"
+	"github.com/mhsanaei/3x-ui/v3/internal/util/maskcompat"
 	"github.com/mhsanaei/3x-ui/v3/internal/util/random"
 	wgutil "github.com/mhsanaei/3x-ui/v3/internal/util/wireguard"
 )
@@ -640,6 +641,8 @@ func (s *SubJsonService) getConfig(subReq *SubService, inbound *model.Inbound, c
 		if finalmask, ok := newStream["finalmask"].(map[string]any); ok {
 			newStream["finalmask"] = withLegacyFragmentRanges(finalmask)
 		}
+		// An inbound keeps its hop range as quicParams.udpHop; clients hop only with the mask.
+		maskcompat.UpgradeLegacyUDPHop(newStream["finalmask"])
 		streamSettings, _ := json.MarshalIndent(newStream, "", "  ")
 		hostMux := hostMuxOverride(extPrxy)
 
@@ -1001,6 +1004,7 @@ func (s *SubJsonService) genHy(inbound *model.Inbound, newStream map[string]any,
 	if finalmask, ok := hyStream["finalmask"].(map[string]any); ok {
 		newStream["finalmask"] = mergeFinalMask(newStream["finalmask"], finalmask)
 	}
+	maskcompat.UpgradeLegacyUDPHop(newStream["finalmask"])
 
 	newStream["network"] = "hysteria"
 	newStream["security"] = "tls"