fix(dev-1711): bump flatted to 3.4.2

[spur-vuln-author]

Context

GHSA-rf6f-7fwh-wjgh: flatted before 3.4.2 is vulnerable (high severity, prototype pollution). Transitive dependency (not declared in any package.json), resolved via pnpm-lock.yaml. No Dependabot PR exists for this finding, so this PR was constructed directly from the advisory's first_patched_version.

Test evidence

No Dependabot PR existed; constructed from first_patched_version 3.4.2. Added a pnpm.overrides entry and regenerated the lockfile with pnpm install --lockfile-only. Confirmed via lockfile inspection that flatted now resolves to 3.4.4 (previously 3.3.3), satisfying >= 3.4.2. Companion-file scan (Dockerfiles, .nvmrc, go.mod, CI workflow YAML, etc. hardcoding 3.3.3) found no hits.

Risk

Low. Lockfile-only transitive dependency bump within the same major version line. GHSA-rf6f-7fwh-wjgh / high severity; Tier 1 / 90-day SLA, currently overdue.

---

[spur-vuln-reviewer]

Escalating: Gate 3 (diff equivalence) mechanically FAILed. gate3-check.sh: GATE3 FAIL target=flatted manifest=pnpm-lock.yaml pr_version=? required=3.4.2 alerts=44 extra_files=1 state=open. Detail: the helper has no extraction rule for ecosystem=npm manifest basename=pnpm-lock.yaml, so it could not extract the new flatted version from the diff, and flagged package.json as a file outside {manifest, lockfile} (which is actually the expected direct-dependency file for an npm/pnpm version bump). This looks like a tooling gap in gate3-check.sh (no pnpm-lock.yaml parser) rather than a real diff deviation, but per the review contract a mechanical Gate 3 FAIL is never re-derived or second-guessed by the reviewer. Required version per max open Dependabot alert(s) 44: 3.4.2. Not merged. A human must review this. This reviewer will not act on this PR again. [[spur-vuln-reviewer: escalated diff-mismatch-constructed]]