test: cover the last unclaimed uncovered regions in three scripts

[hivecommons-hive]

Test Improvement

A merged V8 range analysis of the unit suite (NODE_V8_COVERAGE over
TZ=UTC node --test, unioning every child-process record per source offset)
leaves exactly three reachable uncovered regions in scripts/ that no open PR
claims. Each one guards real behaviour that nothing currently pins. This PR adds
one test per region, using the harnesses the suite already provides.

• tests/collect-case-studies.test.mjs — a data/case-studies.json that lacks
  the caseStudies key is read as an empty list, so the "nothing changed"
  comparison still holds against an empty upstream and the file is left
  byte-for-byte alone instead of getting a fresh generatedAt. Covers
  scripts/collect-case-studies.mjs:23.
• tests/import-architectures.test.mjs — docs/architectures/index.md survives
  an import while a stale imported page beside it is pruned. Covers
  scripts/import-architectures.mjs:79.
• tests/validate-architecture-assets.test.mjs — the shallow static/img walk
  does not descend into a subdirectory that is not an asset root, so an asset
  nested inside one is neither validated nor counted. Covers
  scripts/validate-architecture-assets.mjs:146.

Tests only; no production code is touched. Full suite green (1426 tests),
npm run test:unit:coverage:check passes, and src region coverage rises from
98.46% to 98.63%.

Scope

Claims tests/collect-case-studies.test.mjs, tests/import-architectures.test.mjs
and tests/validate-architecture-assets.test.mjs, and the three script regions
named above. Deliberately disjoint from the open hold-gated PRs: #810 and #812
(scripts/import-architecture-issue.mjs), #818
(scripts/lib/svg-active-content.mjs) and #820
(tests/architecture-catalog-contract.test.mjs).

Related Issue

Closes #824

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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.

[hivecommons-hive]

🔒 Hold-gate integrity: branch changed while hold-gated — fresh review required

This PR's branch moved while it sat hold-gated: the head recorded when the hold was applied was babe85b02ad5, but the branch now sits at c4a0943c5e8f. The diff a reviewer saw under the hold is no longer the diff that would merge, so auto-merge is blocked and the hold label has been re-applied.

Commits not present in the hold-time snapshot (1):

• c4a0943c5e8f by hivecommons-hive[bot] — test: cover the last unclaimed uncovered regions in three scripts

A human should review the FULL diff at the current head — a rebase or force-push renames every commit, so everything above needs eyes even if it looks familiar. Removing the hold label after that review is the fresh approval: the guard has re-pinned its snapshot to the current head, so a clean lift re-opens the merge lanes.