ci(skill): extend npm provenance wait

[yunze7373]

Summary

• Extend the npm package and provenance propagation deadline from 300 seconds to 900 seconds.
• Update the comment to reflect roughly 10-minute registry propagation observed for Skill 1.1.42.
• Leave the separate xmemo.dev 300-second check and all other workflow steps unchanged.

Validation

• Searched test/ and scripts/; no checks pin this npm deadline or the step text.
• git diff --check passed.
• CI will validate this workflow-only change on the PR.

The phase-B release closeout review was submitted as request 0996d8f4-3d50-4251-ac4d-9544da75a588 before starting this task.