hive-gateway: serve the swagger-ui theme via nginx alias, not a c0re build hook

nix/host-modules/hive-gateway/default.nix

@@ -24,6 +24,12 @@ let
   # container's).
   dashboardDist = "${config.services.hyperhive.c0re.servedFrontend}/dashboard";
 
+  # Swagger UI re-theme static override files — nginx `alias`es these
+  # straight from the store over `/api/docs/`, so a theme tweak ships
+  # as a gateway config change (see vhosts.nix's `swaggerThemeLocations`
+  # and nix/packages/swagger-ui-theme.nix).
+  swaggerUiTheme = config.services.hyperhive.c0re.swaggerUiTheme;
+
   # Self-signed TLS is the implicit floor: when neither an operator cert
   # (`tls.certDir`) nor ACME (`tls.acme.enable`) is configured, the gateway
   # generates + serves a hive-CA-signed leaf (see hive-tls.nix). There is no
@@ -261,6 +267,7 @@ in
               matrixCfg
               hyperhiveDomain
               dashboardDist
+              swaggerUiTheme
               tlsCert
               tlsKey
               ;