docs: document pack setup for administrators

[jbouder]

Closes #89.

Adds five administrator pages to the existing Astro + Starlight site on main, covering the four questions the issue asks.

Supersedes #92, which proposed a second, Docusaurus-based docs site. That PR predates #201, which landed the Astro site this repo now uses — its only content was a 10-line placeholder introduction.mdx; the rest was Docusaurus scaffolding and a lockfile. There is nothing in it to port. I'll close it once this is reviewed.

Issue requirements → pages

Issue asks	Where
What are the yaml config options and what does each one do?	Values reference — every field in keycloak, subdomains, nebariapp, singleuser, singleuserCuller, sharedStorage, nebi, rbac.bootstrap, jupyterhub.custom, plus the upstream passthrough
How do I integrate nebi to this?	Nebi integration
How do I integrate MLflow to this?	MLflow integration
General JHub setup (server sizes, etc.)	Server profiles
(setup itself)	Admin setup — prerequisites, the derivation model, what the chart creates, verification

Deliberately not reinventing other open docs PRs

I read the open docs: PRs first and scoped around them:

PR	Adds	How this PR relates
#204	nebi-in-jupyterlab.md — Nebi user workflows	My Nebi page is the admin side (images, OIDC clients, token exchange, registries, NetworkPolicies) and links out to #204 rather than restating it
#139	gpu-profiles.md — GPU requests, tolerations, the replace-not-append trap	Server profiles covers the general profile model and defers the GPU specifics to #139 with a link
#219	gallery.md + one row in configuration.md	Untouched
#142	examples/ values + ArgoCD app	Untouched

To keep those mergeable, edits to existing pages are additive only: configuration.md gains a "Detailed guides" list appended below its table (#219 adds a row to the table, so no overlap), and index.md gains an Administration section. Neither is restructured.

Content came from the chart, not the README

Everything is derived from values.yaml, templates/, _helpers.tpl, and config/jupyterhub/*.py, so derivation rules and defaults match what actually renders. Three things get explicit callouts because they fail quietly:

1. jupyterhub.hub.extraVolumes / extraVolumeMounts replace on override. Both carry custom-config (the jupyterhub_config.d ConfigMap) and oauth-client (the OIDC Secret). Override either without re-including them and the hub comes up with an empty config directory and dummy auth. The values file warns about this; it now appears in Admin setup and Values reference too.

2. The base domain is keycloak.hostname minus its first label. A single-label value derives an empty hub hostname, Nebi URL, and token URL — the chart renders fine and nothing routes.

3. The MLflow NetworkPolicy must name port 5000, not 80. z2jh defaults singleuser.networkPolicy.egressAllowRules.privateIPs: false, so user pods can't reach in-cluster services at all without an explicit rule — and the rule is evaluated after kube-proxy has translated the ClusterIP, so a rule written against the Service port matches nothing and every connection times out silently.

Two smaller things worth flagging from reading the code:

• mlflow is not in the JupyterLab image (images/jupyterlab/pixi.toml). Setting MLFLOW_TRACKING_URI alone does nothing — import mlflow fails. The page says so and shows the Nebi/pixi and pip routes.
• jupyterhub.custom.storage-capacity (home PVC size, default 20Gi) is read by 01-spawner.py but isn't in values.yaml. It's documented in the Values reference; adding it to values.yaml with its default would be a reasonable follow-up.

Also

Adds a Documentation section to the README, which had no link to the published docs site. Placed before ## License so it doesn't collide with #139's README edit in the Configuration section.

Verification

npm test               9 passed
npm run build          12 pages, pagefind index built
check-links.sh         LINKS_OK at BASE=/ and BASE=/data-science-pack/

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Docs preview for docs/admin-setup:
https://docs-admin-setup.data-science-pack.pages.dev