9cb44fc70c
Adds src/lib/tag/__fixtures__/cross-domain.fixture.ts — a permanent fixture that demonstrates the boundaries rule firing on a tag → person import. The fixture is excluded from npm run lint via --ignore-pattern; run npm run lint:boundary-demo to see it produce an error (exit 1). Documents the full allow-list, the escape hatches ($lib/shared/ move, explicit rule entry, eslint-disable-next-line), and the verify command in COLLABORATING.md. Refs #410 Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>