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.

.dockerignore

@@ -14,8 +14,6 @@ ops/cookbooks/
 ops/roles/
 ops/proxy.service
 
-# Docs site (served via GitHub Pages, not from the image).
-docs/
 .github/
 
 # Git + editor + secrets.
@@ -24,8 +22,13 @@ docs/
 # nodejs/utils/build_info.js), then it's discarded before the final stage.
 # It never ends up in the final image.
 .gitignore
+# docs/ and the doc files below ARE needed in the image now — served in-app
+# at /docs (routes/docs.js) so they're readable without internet access.
 *.md
 !README.md
+!DEPLOYMENT.md
+!nodejs/api.md
+!docs/**/*.md
 secrets.js
 secrets.json
 *.env