chore(deps): Upgrade js-yaml to v5

[jkowall]

Summary

• upgrade scripts/reorg-docs from js-yaml v4 to v5
• migrate the ESM consumer from the removed default export to named load and
  dump exports
• remove the obsolete @types/js-yaml package because v5 ships its own types
• add a dedicated CI job for the reorganization tool
• replace a stale title assertion with a front-matter validity check

Why

The dependency can move to the current major with a small source migration.
The existing test suite covers both parsing and serialization against real
documentation content, and it passes with js-yaml 5.2.1.

This is the v5 alternative to #1117. The v4 draft remains open so the two
approaches can be compared before choosing one.

Validation

• scripts/reorg-docs: npm run build
• scripts/reorg-docs: npm test -- --runInBand, 9 suites passed, 49 tests
  passed, 2 skipped
• npm run build
• npm run check:format
• npm run check:spelling
• npm run check:links:internal

[yurishkuro]

The change seems trivial, why wouldn't we go for new major?