feat(#3255): expose the controller's webhook endpoint through the swarm vhost

A forge webhook is a machine POST carrying an HMAC and no session cookie,
so it cannot pass the authelia auth-request subrequest every other location
on this vhost uses. This location deliberately omits it; the HMAC check in
the controller is what guards the path.

Scoped to /webhook/forge/ rather than /webhook/ so a future endpoint under
the same prefix does not inherit the bypass.

nix/host-modules/swarm-ui.nix

@@ -188,6 +188,27 @@ in
             proxyPass = "http://unix:${controllerCfg.socketPath}:";
             extraConfig = swarmAuthRequest;
           };
+          # ⚠️ THE ONE LOCATION ON THIS VHOST WITH NO `swarmAuthRequest`,
+          # and that is deliberate rather than an omission.
+          #
+          # A forge webhook is a machine POST carrying an HMAC signature
+          # and no session cookie. An authelia auth-request subrequest
+          # authenticates a *browser session*; there is nothing here for it
+          # to check, so guarding this location would not make it safer, it
+          # would make it permanently unreachable.
+          #
+          # What replaces it: swarm-controller verifies the
+          # `X-Hub-Signature-256` HMAC over the raw body before looking at
+          # anything else, and answers 401 on any mismatch. That check is
+          # the access control for this path — see the `webhook` module.
+          #
+          # Scoped to `/webhook/forge/` rather than `/webhook/` so the
+          # carve-out is exactly as wide as the endpoint that justifies it:
+          # a future `/webhook/<something-else>` does not inherit the
+          # bypass by living under a shared prefix.
+          "/webhook/forge/" = {
+            proxyPass = "http://unix:${controllerCfg.socketPath}:";
+          };
           # Swagger UI: same "nginx hosts the themed dist straight from
           # the store, only /api/openapi.json is dynamic" shape as the
           # per-hive gateway's `swaggerUiLocations`.