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/app.js

@@ -77,6 +77,11 @@ app.use('/__proxy_auth', require('./routes/host_auth'));
 // Routes for front end content.
 app.use('/', require('./routes/render'));
 
+// Local, in-app copy of the project's documentation (README, DEPLOYMENT,
+// api.md, docs/*) -- public, no auth, so it's readable even by a locked-out
+// admin or an air-gapped operator with no route to GitHub Pages.
+app.use('/docs', require('./routes/docs'));
+
 // Routes for API
 app.use('/api', require('./routes/api'));