Canon auto-detect fallback (e.g. '1 Nephi 3:150' → COC) #4

Master returns empty verse_ids when a verse number exceeds the default canon but exists in another (e.g. 1 Nephi 3:150 exists in COC, not LDS).

A first implementation lives on tag archive/yaml-refactor (commit "feat: implement auto-detect canon fallback"), with a spec in test/integration/auto-detect-canon.test.js. That branch predates master's YAML pipeline and conflicts heavily, so reimplement on current code (likely alongside the cross-canon WIP) and reuse the tests as the spec.