Air-gap: remove dead CDN reference + in-app /docs

- Removed a dead IE<9-only html5shim script tag pointing at a domain
  that no longer resolves.
- New GET /docs (index) and /docs/:slug routes render this project's
  own README, DEPLOYMENT, API.md, docs/*.md, and directory_spec.md
  server-side via marked -- so the documentation is readable from the
  running app with no route to GitHub Pages, where it otherwise only
  lives. Public, no auth, rate-limited (middleware/rate_limit.js) like
  the other public routes.
- .dockerignore/Dockerfile.openldap updated to copy DEPLOYMENT.md,
  API.md, directory_spec.md, and docs/ into the image, mirroring the
  existing tos.md -> /tos.md convention.

nodejs/views/docs_index.ejs

@@ -0,0 +1,24 @@
+<%- include('top') %>
+<div class="row justify-content-center">
+	<div class="col-md-8">
+		<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="card-body">
+				<p class="text-muted">
+					A local copy of this project's documentation, readable from the
+					running app -- no internet access required.
+				</p>
+				<ul class="list-group">
+					<% docs.forEach(function(doc){ %>
+						<li class="list-group-item">
+							<a href="/docs/<%= doc.slug %>"><%= doc.title %></a>
+						</li>
+					<% }) %>
+				</ul>
+			</div>
+		</div>
+	</div>
+</div>
+<%- include('bottom') %>