docs: update 1-9-sandbox-environments.md

[habib424]

Drafted by Ship Ship 🚢 — confidence 🟢 high

What changed

Added a new subsection "Resetting a sandbox" under "Managing sandboxes" explaining the three reset modes (Reset to template, Wipe transactions only, and Wipe all data) accessible from the row menu on active sandboxes. Added an FAQ entry explaining when to use each reset mode. The reset action cannot be undone.

Source PRs

• axolotl#4250 — feat(sandbox): reset action on the sandboxes screen

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.