fix(docker): nginx healthcheck uses 127.0.0.1 not localhost — IPv4-only listener

corrosion-nginx reported (unhealthy) despite serving the panel fine:
nginx listens 0.0.0.0:80 (IPv4 only, no listen [::]:80), but
'localhost' resolves to ::1 first inside the container, so the probe
got connection-refused. Verified: 127.0.0.1:80 serves the SPA. Probe
now targets IPv4 explicitly. No nginx config change — the panel was
never broken, only the healthcheck's hostname resolution.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docker/docker-compose.yml

@@ -87,7 +87,10 @@ services:
       api:
         condition: service_started
     healthcheck:
-      test: ["CMD-SHELL", "wget -q --spider http://localhost:80/ || exit 1"]
+      # 127.0.0.1, not localhost: nginx listens IPv4-only (0.0.0.0:80) but
+      # `localhost` resolves to ::1 first inside the container → the probe hit
+      # nothing and reported unhealthy while the panel served fine on IPv4.
+      test: ["CMD-SHELL", "wget -q --spider http://127.0.0.1:80/ || exit 1"]
       interval: 10s
       timeout: 5s
       retries: 3