Add healthcheck to Gitea (/api/healthz)

Gitea exposes /api/healthz unauthenticated. 60s start_period
because Gitea sqlite migration on cold start can take a while.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

core/gitea/docker-compose.yml

@@ -26,6 +26,12 @@ services:
       - "222:22"
     networks:
       - frontend_net
+    healthcheck:
+      test: ["CMD-SHELL", "wget -q --spider http://localhost:3000/api/healthz || exit 1"]
+      interval: 30s
+      timeout: 5s
+      retries: 5
+      start_period: 60s
     labels:
       - "traefik.enable=true"
       - "traefik.docker.network=frontend_net"