ci: serve /healthz over IPv4 for nginx healthcheck

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: chr-hertel

tests/Conformance/Fixtures/docker-compose.yml

@@ -11,7 +11,7 @@ services:
     networks:
       - mcp-net
     healthcheck:
-      test: ["CMD", "wget", "-q", "-O-", "http://localhost/"]
+      test: ["CMD", "wget", "-q", "-O-", "http://127.0.0.1/healthz"]
       interval: 2s
       timeout: 2s
       retries: 10

tests/Conformance/Fixtures/nginx.conf

@@ -3,6 +3,11 @@ server {
     server_name localhost;
     root /app;
 
+    location = /healthz {
+        access_log off;
+        return 200 "ok\n";
+    }
+
     location / {
         try_files $uri /tests/Conformance/server.php$is_args$args;
     }