chore: replace stale draft with canonical ts-TEMPLATE form for ts-homepage

- Replace alternate template form (with {{YOUR_TAILSCALE_AUTHKEY}}, sys_module
  cap, hardcoded homepage.damconsulting.net serve.json) with the canonical
  ts-TEMPLATE pattern: Tailscale sidecar + Homepage, both via network_mode
- Use named volume for config dir; default settings/services/bookmarks/widgets
  files included as starting points for the user to customize
- Add SECURITY.md and proper .gitignore (incl. Homepage's auto-generated
  custom.css/custom.js/docker.yaml/kubernetes.yaml/proxmox.yaml stubs +
  logs/)
- serve.headscale.json now uses the actual MagicDNS base domain
  (homepage.damconsulting.net) so the user has a working starting point
  to edit, not a {{service}} placeholder that doesn't resolve
- Verified: dashboard renders at homepage.damconsulting.net

homepage/config/settings.yaml

@@ -0,0 +1,14 @@
+---
+# Homepage settings: https://gethomepage.dev/configs/settings/
+# Background, theme, layout, color scheme
+
+title: DAM Homelab
+background:
+  opacity: 50
+  blur: sm
+  saturation: 100
+theme: dark
+color: slate
+headerStyle: underlined
+favicon: https://gethomepage.dev/icon.png
+