test: cover the /community/technical-community-groups generated index end to end

[hivecommons-hive]

Test Improvement

Adds tests/e2e/technical-community-groups.spec.js — the only file this PR
touches.

/community/technical-community-groups is a generated-index route:
docs/community/technical-community-groups/_category_.json declares
link.type: "generated-index", so the page has no source document. Docusaurus
synthesises the <h1> and the blurb from that JSON, and one card per doc in
the directory from each doc's frontmatter title, description and slug.

Because nothing on disk holds the rendered result, no unit test can assert it —
and no e2e spec loaded it. At main @ 7772dcf the string
technical-community-groups did not appear anywhere under tests/.
npm run test:unit:coverage cannot see the gap either: it reports
src files | 99.84 | 98.46 | 6329/6339 lines while this route is entirely
unexercised, because a generated index contributes no executable source lines
of its own.

The route is not incidental — docs/community/index.md:30 and :87 and
docs/community/technical-advisory-board.md:15 all link to it as the way a
visitor finds a topic group. Moving a doc out of the directory, renaming a
slug, or dropping a frontmatter description would empty or mislabel the
page while every existing test stayed green.

The 8 tests assert that:

• the route serves — status < 400 and not the "Page Not Found" page, since
  docusaurus serve answers an unknown path with the 404 page
• the <h1> and the header blurb are the link.title / link.description
  from _category_.json. Those two strings exist nowhere else; if the file is
  renamed or loses its link block, Docusaurus falls back to the directory
  name and drops the blurb, in a build that stays green
• the autogenerated communitySidebar and the breadcrumb trail still render —
  a generated index that drops out of the sidebar is reachable only by typing
  the URL
• there is exactly one card per doc in the directory
• each card carries its doc's frontmatter title and description verbatim
  and links to the slug that doc declares
• clicking a card lands on that slug and renders the leaf's own <h1> — which
  is written in the leaf body rather than derived from frontmatter, so this
  catches an empty shell as well as a 404
• the index and its leaves are listed in sitemap.xml, compared as parsed
  pathnames so a substring cannot pass for a different route

Expectations are read from _category_.json and the leaf frontmatter rather
than hardcoded, so a newly added TCG is covered on arrival instead of needing
this file edited. A fixture guard fails loudly if the directory ever stops
yielding docs, which would otherwise turn the per-leaf cases into zero tests.

Disjointness

• test: cover /resources, /community/governance and the platform-engineering TCG page end to end #829 covers the platform-engineering leaf page; this PR covers the
  index that lists it. Different route, different spec file.
• test: cover the /community/user-groups generated index end to end #840 covers the /community/user-groups generated index and its own
  _category_.json; this is the sibling TCG directory, untouched by it.
• No file in this PR is touched by any other open PR.

Verification

Against main @ 7772dcf: npm ci, npm run build:production, then
npx playwright test tests/e2e/technical-community-groups.spec.js — 8
passed. npm run test:unit:coverage:check still exits 0.

Checked non-vacuous by mutating link.description in _category_.json,
rebuilding, restoring the JSON and re-running against the drifted build: the
description assertion failed with element(s) not found, and went green again
after a clean rebuild.

Note for reviewers running this locally: playwright.config.js serves build/
and sets reuseExistingServer, so a stale docusaurus serve already bound to
port 3000 will be reused and your results will describe its build rather than
yours. Set E2E_PORT if that is a possibility.

Related Issue

Closes #843

---

Filed by quality agent (hold-gated mode). Human review required.

— hive: agent=quality backend=copilot model=claude-opus-5 copilot=1.0.88

[hivecommons-hive]

Important

Held for human review by the hive's ACMM level gate.

This PR was opened by the "quality" agent while Hive policy required a human checkpoint for that agent. Non-outreach agents are held at ACMM L3–L5; the outreach agent is always held because it publishes project-facing communication.

Hive will automatically remove the hold label once current policy no longer requires a level hold for "quality". If this is an outreach PR, a human must review it and remove the label.