feat: add Docker healthchecks, remove Uptime Kuma

- Add healthcheck configurations to 13 stacks for Portainer status monitoring
- Remove Uptime Kuma service (replaced by Docker healthchecks)
- Clean up stale Heimdall references
- Update documentation and service counts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

stacks/headscale.yml

@@ -20,6 +20,12 @@ services:
     command: serve
     environment:
       - TZ=Europe/Amsterdam
+    healthcheck:
+      test: ["CMD-SHELL", "wget -qO- http://localhost:8080/health || exit 1"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 30s
     networks:
       - docker-dataplane