Eliminate legacy gateway container (consolidate into router-gateway)

The gateway service was a redundant deployment of the same
StellaOps.Gateway.WebService binary already running as router-gateway.
It served no unique purpose — all traffic is handled by router-gateway
(slot 0). This removes the container, its route table entries, nginx
proxy blocks, health/quota stubs, and redirects STELLAOPS_GATEWAY_URL
to router.stella-ops.local so the Angular frontend resolves API base
URLs through the canonical frontdoor.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

devops/compose/router-gateway-local.reverseproxy.json

@@ -591,11 +591,6 @@
                                        "Path":  "/envsettings.json",
                                        "TranslatesTo":  "http://platform.stella-ops.local/platform/envsettings.json"
                                    },
-                                   {
-                                       "Type":  "ReverseProxy",
-                                       "Path":  "/gateway",
-                                       "TranslatesTo":  "http://gateway.stella-ops.local"
-                                   },
                                    {
                                        "Type":  "ReverseProxy",
                                        "Path":  "/scanner",