docs: update 5-2-document-types-lifecycle.md

[habib424]

Drafted by Ship Ship 🚢 — confidence 🟢 high

What changed

Added a brief note in the Archival section explaining that archived invoice receivables and customer credits can be unarchived back to DRAFT status, completing the lifecycle description without diving into API-specific implementation details.

Source PRs

• light#6672 — Allow unarchiving sales invoices and customer credits

How to use this PR

1. Review the diff against the existing article — focus on accuracy and customer voice.
2. Merge if it reads well. Edit and push to this branch if it needs adjustment.
3. Close without merging if the article doesn't actually need this update.

Once we have a track record of clean drafts, we'll graduate to auto-merge with a delay buffer. For now: human-in-the-loop.