ci(schema): enforce locale-tag refs - #6444

Ladon verdict: Escalate to human review

Escalate — gated path touched and required review not yet satisfied.

This PR adds a high-recall JSON Schema lint (scripts/lint-language-tag-refs.cjs), a typed disposition registry, focused tests, a package.json npm script, and a Build Check workflow step. The reviewer found no actionable issues: no static/schemas/source/**, dist/**, wire-shape, or package.json version changes, so schema-drift, changeset, oneOf, and immutability rules do not apply. Control flow of the lint script is fail-closed and verified against tests. Clean diff.

However, .github/workflows/build-check.yml (modified) matches the gated glob .github/workflows/**, so gated_paths: true, and review_decision is REVIEW_REQUIRED (not APPROVED). Per decision-table row 2, this is a hard, non-overridable approval gate that must not be auto-approved until a human/CODEOWNERS review is recorded.

No blocking findings exist — the escalation is purely the gated-path requirement.

Escalation reasons

• .github/workflows/build-check.yml (modified) is under the hard approval gate (.github/workflows/**); review_decision is REVIEW_REQUIRED. Human/CODEOWNERS approval required before merge.

Why human review

• Modifies .github/workflows/build-check.yml — matches gated path .github/workflows/**, and review_decision is REVIEW_REQUIRED (not APPROVED). Requires human/CODEOWNERS review.
• This PR touches a path under a hard, non-overridable approval gate (.github/workflows/build-check.yml (modified) matches .github/workflows/**) and the current GitHub review decision is 'REVIEW_REQUIRED', not APPROVED. This is a hard gate enforced in code — Ladon cannot auto-approve until a human/CODEOWNERS approval is recorded, regardless of how clean the diff is.