fix: comment export to merge fragmented marks per commentId

[financialvice]

Summary

• merge all commentMark slices per commentId (and child comments) into one min..max range before export
• insert a single commentRangeStart/End pair per id, using transaction mapping for correct positions after prior inserts
• add a unit test covering fragmented marks exporting as one contiguous range

Background

Previously, prepareCommentsForExport would emit range nodes using only the first encountered slice for a commentId. When a commentMark spanned multiple adjacent text nodes, the exported DOCX/round-trip highlight was truncated. This change collects min..max spans and emits a single start/end pair, preventing truncated anchors.

Testing

• npm run build:super-editor
• npm run test:editor

---

disclaimer, generated primarily by gpt-5.1-codex-max

[harbournick]

@chittolinag related to our discussion today. Mind checking this one out?

[chittolinag]

@chittolinag related to our discussion today. Mind checking this one out?

yes - I'll review this one today.

[chittolinag]

Hey @financialvice - thanks for submitting the PR here! Can you please share the document you reproduced the issue? Just by reading the PR description + code, I can't really tell what exactly is being fixed - it will be easier with a real example. Also, I'm working on something possibly related so just wanna double check whether your PR fixes my issue or my PR fixes yours 🙂

Thank you!