fix(sub): default VLESS client encryption to none when the inbound has none stored (#6781)

VLESS inbounds whose settings carry no "encryption" key (rows saved by
panels before the field existed, or inbounds added over the API with only
"decryption":"none", as the API docs example does) produced a JSON
subscription outbound with "encryption": "". Xray refuses to load that
config ("VLESS users: please add/set \"encryption\":\"none\" for every
user"), so every VLESS entry of the JSON subscription was unusable. The
share link left the parameter out instead.

Treat a missing or empty value as "none" for both outputs, matching the
frontend inbound schema default and the docs link generator.

internal/sub/json_service.go

@@ -885,15 +885,11 @@ func (s *SubJsonService) genVless(subReq *SubService, inbound *model.Inbound, st
 	}
 	outbound.StreamSettings = streamSettings
 
-	// Add encryption for VLESS outbound from inbound settings
-	inboundSettings := subReq.linkSettings(inbound)
-	encryption, _ := inboundSettings["encryption"].(string)
-
 	settings := map[string]any{
 		"address":    inbound.Listen,
 		"port":       inbound.Port,
 		"id":         client.ID,
-		"encryption": encryption,
+		"encryption": vlessClientEncryption(subReq.linkSettings(inbound)),
 		"level":      8,
 	}
 	if client.Flow != "" && !inbound.DisableFlow {