Air-gap fixes + in-app /docs (README/DEPLOYMENT/api.md/docs/*)

Air-gap:
- DynamicRecord.refreshAll() called getPublicIp() (api.ipify.org,
  icanhazip.com, ifconfig.me) every 4h on a timer regardless of
  whether any dynamic records were configured -- the one background
  call in the repo not actually gated by feature use. Now skips the
  lookup entirely when there's nothing to refresh.
- Removed the stray, unauthenticated GET /test page (a leftover
  jq-repeat demo) that loaded jQuery + Mustache from external CDNs.
- Removed a dead IE<9-only html5shim script tag pointing at a domain
  that no longer resolves.

Docs:
- New GET /docs (index) and /docs/:slug routes render this project's
  own README, DEPLOYMENT, api.md, and docs/*.md server-side via
  marked (new dependency) -- so the documentation is readable from
  the running app with no route to GitHub Pages, where it otherwise
  only lives. Public, no auth, same tier as the health endpoint.
- .dockerignore/Dockerfile updated: docs/, DEPLOYMENT.md, and
  nodejs/api.md were previously excluded from the image entirely
  ("served via GitHub Pages, not from the image") -- now copied in
  alongside README.md/tos.md-style, since they're needed at runtime.

nodejs/views/docs_page.ejs

@@ -0,0 +1,31 @@
+<%- include('top') %>
+
+<div class="row">
+	<div class="col-md-3 d-none d-md-block">
+		<div class="card shadow-lg mt-4 mb-4">
+			<div class="card-header shadow">
+				<i class="fa-solid fa-book"></i> Documentation
+			</div>
+			<div class="list-group list-group-flush">
+				<% docs.forEach(function(doc){ %>
+					<a href="/docs/<%= doc.slug %>"
+						class="list-group-item list-group-item-action<%= doc.slug === currentSlug ? ' active' : '' %>">
+						<%= doc.title %>
+					</a>
+				<% }) %>
+			</div>
+		</div>
+	</div>
+	<div class="col-md-9">
+		<div class="card shadow-lg mt-4 mb-4">
+			<div class="card-header shadow">
+				<i class="fa-solid fa-file-lines"></i> <%= docTitle %>
+			</div>
+			<div class="card-body markdown-body">
+				<%- docHtml %>
+			</div>
+		</div>
+	</div>
+</div>
+
+<%- include('bottom') %>