* fix(skills): keep custom-skill edit checks off the event loop
update_custom_skill built the user-scoped storage, ran the editability
probes, validated the frontmatter through a temporary directory and read
the content being replaced on the Gateway loop; only the write and history
append had been offloaded. Run the pre-scan checks in one worker and the
replaced-content read in another, matching rollback_custom_skill, and build
delete_custom_skill's storage off the loop as well.
* fix(skills): build skill storage off the loop in install and skill_manage
The same sweep that moved the custom-skill edit checks off the loop finds
two more storage lookups on it: the archive-install helper behind both
install routes, and the agent's skill_manage tool, whose lookup resolves
and stats config.yaml on every call. Offload both, and pin that the
caller's user context still reaches the storage lookup now that the edit
route resolves it inside a worker.
* docs(changelog): reference #6332 for the skill storage off-loop fix
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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
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