Point the docs index at the current site, and index the docs

[Robbie1977]

Why

The task battery failed on T3.8 because get_reviewed_page fetched
https://v2.virtualflybrain.org/circuit-browser and got a 404. There is no such
page — the model constructed it, because the index had nothing about the Circuit
Browser and the only v2. URL it had seen was the Geppetto viewer. Any path on
an allow-listed host is fetchable, so a plausible guess gets tried.

The underlying problem is bigger than one task: the index held 13 entries, two of
which were documentation pages. The site publishes 77 pages under /docs/. Asked
how to use any part of the site, the model had almost nothing to read.

Corrections

• Home page pointed at the bare host. hugo.toml sets
  baseURL = "https://www.virtualflybrain.org/", so the bare form is not
  canonical and answered a 302 — to http, at that.
• 3D viewer pointed at the v2 single-page app, which serves no readable text.
  The site documents the viewer properly now, so it points there.
• /reports/ removed. It is a routed namespace rather than a document: bare
  /reports/ redirects into the Geppetto app, so there is nothing to review. It
  belongs in the outbound allow-list, where linking is decided, not in an index
  of pages to read.

Additions

The whole Website Features section — search and query, 3D viewer, slice
viewer, term info, term context, thumbnails, circuit browser — plus a landing
page for each of Concepts, Data, Tutorials, APIs, Anatomy Diagrams, Resources and
Overview, so there is an entry point into every part of the documentation rather
than a guess.

Titles and summaries are taken from each page's own front matter in the VFB2
wrapper site rather than written here, so they stay true to the page.

Not addressed here

This removes most of the reason for the model to invent a URL; it does not stop
it. get_reviewed_page will still fetch any path on an allow-listed host.
Constraining it to indexed URLs is the actual fix, and it is the same shape as
the existing grounding rule for identifiers — worth its own change rather than
folding a behaviour change into a data update.

Verification

• All 27 URLs fetched with redirect: 'manual' — every one returns 200 with no
  redirect.
• node --test tests/unit/*.test.mjs — 1277 pass, 0 fail.