Add mdBook infra runbook served by Caddy on control

Docs live in docs/ (DNS, ZeroTier mesh, monitoring), built at Nix-build time and
served as static files over the ZeroTier mesh on control:8080. Commit-to-edit:
change the markdown and redeploy to publish.

docs/book.toml

@@ -0,0 +1,12 @@
+[book]
+title = "CNX Infra Runbook"
+description = "Operational docs for the cnx-network clan: DNS, ZeroTier mesh, monitoring."
+authors = ["B4L"]
+src = "src"
+language = "en"
+
+[output.html]
+default-theme = "navy"
+preferred-dark-theme = "navy"
+git-repository-url = "https://git.b4l.co.th/B4L/cnx-network-clan"
+edit-url-template = "https://git.b4l.co.th/B4L/cnx-network-clan/_edit/main/docs/{path}"