test: pin the four architecture-content exports no test names

[hivecommons-hive]

Test Improvement

Adds tests/architecture-content-helpers.test.mjs (15 tests), pinning the four
exports of scripts/lib/architecture-content.mjs that no test in the repository
names: splitFrontmatter(), listValue(), renderProjectCards() and
firstParagraph().

The other two exports of that module each already have a test file —
cleanMarkdown() in tests/architecture-content-clean-markdown.test.mjs,
mirrorArtworkUrls() in tests/architecture-content-mirror.test.mjs. These four
were reached only transitively, through scripts/import-architectures.mjs and
scripts/import-architecture-issue.mjs, so they scored 100% region coverage while
nothing stated what they return. A behavioural change inside them moved no test as
long as the importer still finished.

What is now asserted:

• splitFrontmatter — a --- block parses and the body is trimmed; text with
  no block is valid input returning { frontmatter: {}, body: text }; an empty
  block yields {} rather than the null yamlParse('') returns.
• listValue — list passes through, scalar wraps, undefined/null/''
  give [], and the truthiness guard means a numeric 0 or false also gives
  [].
• renderProjectCards — a full {{< card >}} shortcode renders every
  attribute; a non-CNCF link never becomes the card href (the
  isCncfProjectHref() rejection falls back to a slug of the card header); a card
  with no link uses that same fallback; a " in upstream prose is JSON-escaped
  inside the expression attribute rather than terminating it and opening a new
  prop; an unresolvable logo is omitted rather than left pointing off-site; several
  cards are all rewritten with surrounding prose untouched; a body with no
  shortcode is returned unchanged.
• firstParagraph — headings, images and markup are skipped; nothing
  qualifying returns ''; the summary is capped at 240 characters.

Both call sites are unattended importers of third-party text — a cncf/architecture
clone and a GitHub issue form — which is why the two renderProjectCards cases
above are the load-bearing ones.

No production code changes; one new test file.

Verification

Revision 365e11f (main), clean checkout, npm ci, node v26.10.0:

• node --test tests/architecture-content-helpers.test.mjs → 15 passed, 0 failed.
• npm run test:unit:coverage:check → passes. src files goes from
  2713/2713 to 2729/2729 regions at 100.00%: 16 regions that previously
  existed only as incidental importer execution are now directly asserted.
• npx prettier --check and npx cspell lint clean on the new file.

Scope / overlap

Touches tests/architecture-content-helpers.test.mjs only — a new file. Disjoint
from every open hold-gated PR: #1250 (package.json,
tests/coverage-gate-thresholds.test.mjs), #1252, #1262, #1266, #1269, #1273,
#1260 and the three fix(security) PRs touch no file in this cluster, and none of
them names architecture-content.

Related Issue

Closes #1274

---

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 keep the hold label until a human removes it. Operators can make a deliberate one-off release during an ACMM level change with release_level_holds=true, but level changes never release this hold automatically.