update skill step 11 says nothing is lost by removing the snapshot directory; it can hold work the pins cannot rebuild

[realmarcin]

From the round-3 review of #216.

Where: .claude/skills/update-xmech-page/SKILL.md, step 11.

Step 11's guard checks only that revisions.json, mechs/ and claw/ exist, then removes the whole directory, and the step says nothing is lost. In practice the directory collects work that is not snapshot data. This session's refresh/ holds:

• build_site_audit.py, the only copy of the site-audit builder (filed separately);
• the upstream-issue drafts and records;
• review records;
• the stage logs behind the step 4 timings.

Fix: before rm -rf, list any top-level entries other than revisions.json, mechs/, claw/ and logs, and stop for a decision if there are any. Also tell the refresh to keep working files outside $SNAP.