feat(xray): add loopback outbound protocol

#4185
Surface xray-core's loopback outbound in the Outbounds form so users
can re-route already-processed traffic back into a named inbound for
secondary routing (e.g. splitting TCP/UDP from one ingress). The
inboundTag field is an autocomplete over existing inbound tags, with
free-text fallback for inbounds defined outside the panel. Loopback
outbounds are excluded from the connectivity test since they have no
network endpoint.

frontend/src/pages/xray/XrayPage.vue

@@ -294,6 +294,7 @@ function confirmRestart() {
                         :template-settings="templateSettings"
                         :outbounds-traffic="outboundsTraffic"
                         :outbound-test-states="outboundTestStates"
+                        :inbound-tags="inboundTags"
                         :is-mobile="isMobile"
                         @reset-traffic="resetOutboundsTraffic"
                         @test="onTestOutbound"