feat(xray): default outbound in basic routing (#5815)

* feat(xray): default outbound picker in basic routing

Let panel users choose which outbound handles unmatched traffic by
moving it to the first position in the template outbounds list.

* fix(xray): keep direct/blocked outbounds when changing default

* style(routing): revert incidental whitespace churn

Drop double blank lines and the reformatted function signature so the default-outbound diff stays focused on behavior.

internal/web/translation/en-US.json

@@ -1983,7 +1983,9 @@
         "edit": "Edit Fake DNS",
         "ipPool": "IP Pool Subnet",
         "poolSize": "Pool Size"
-      }
+      },
+      "defaultOutbound": "Default Outbound",
+      "defaultOutboundDesc": "Traffic that does not match any routing rule uses this outbound (Xray uses the first outbound in the list)."
     }
   },
   "tgbot": {