fix(dev-1698): bump browserslist to 4.28.7

[spur-vuln-author]

Context

GHSA-73wf-gq98-2v4g: browserslist before 4.28.7 is vulnerable (high severity, ReDoS). 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 4.28.7. Added a pnpm.overrides entry and regenerated the lockfile with pnpm install --lockfile-only. Confirmed via lockfile inspection that browserslist now resolves to 4.29.3 (previously 4.24.4), satisfying >= 4.28.7. Companion-file scan (Dockerfiles, .nvmrc, go.mod, CI workflow YAML, etc. hardcoding 4.24.4) found no hits.

Risk

Low. Lockfile-only transitive dependency bump within the same major version line. GHSA-73wf-gq98-2v4g / high severity; Tier 1 / 90-day SLA.

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[spur-vuln-reviewer]

Escalating: Gate 3 (diff equivalence) mechanically FAILed. gate3-check.sh: GATE3 FAIL target=browserslist manifest=pnpm-lock.yaml pr_version=? required=4.28.7 alerts=115 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 browserslist 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) 115: 4.28.7. Not merged. A human must review this. This reviewer will not act on this PR again. [[spur-vuln-reviewer: escalated diff-mismatch-constructed]]