Fix detached transcript words after DOM edits

[happykawayigt]

Summary

Fixes #265 by keeping transcript playback alive when a cached word has been detached from the DOM and by exposing a supported way for editors to rebuild transcript caches after mutations.

Changes

• guard the active parent update when a cached word no longer has a parentNode
• add public refreshWords() to rebuild wordArr and parentElements
• reset prevWordIndex, activeWordElement, and activeParentElement during refresh
• update the generated ESM build and TypeScript declaration
• add regression coverage for detached cached words and post-edit cache rebuilding

Validation

• node scripts/build-mjs.js
• full Jest suite: 3 suites passed, 76 tests passed
• git diff --check