feat(meta): 抽出技能目錄同步與引用查找為共用工具

什麼：新增 tools/sync-skill-manifest.sh（重建 domain README 的「Skills 目錄」區塊並將三份 plugin manifest 的版本一併 bump）與 tools/find-skill-refs.sh（掃描所有 jsc domain 存取庫，列出技能名稱或 /jsc-{domain}:{name} 指令形式的引用檔案），並更新 skill-check、skill-delete、skill-new、skill-update、skillset-update 五支 SKILL.md 改為呼叫這兩支工具。skill-delete 與 skill-update 的 frontmatter description 也一併收斂在此次改動內，配合本次流程調整精簡文字。
為何：五支技能先前各自以近乎相同的內嵌文字描述「同步 README、bump 版本」的機械流程，重複維護成本高且容易漂移；skill-delete 的引用盤點步驟先前只是一段沒有工具、也沒有標明子代理人的裸 grep 指示，稽核時難以驗證涵蓋範圍。
如何：把兩段機械流程各自抽成一支冪等 shell 工具，五支技能的對應步驟改為「子代理人只做內容判斷與修改，機械式同步與版本 bump 一律呼叫工具」；skill-delete 步驟 4 改呼叫 find-skill-refs.sh 取代裸 grep 說明。
負責範圍：jsc-meta 技能組自我管理，skill-check、skill-delete、skill-new、skill-update、skillset-update 五支技能共用的機械流程去重。

skills/skill-check/SKILL.md

@@ -12,6 +12,6 @@ Single source of guidelines: [`../../references/guidelines.md`](../../references
 1. Query the Gitea canonical marketplace for the authoritative domain list: run `jsc-gitea/tools/gitea.sh api GET /repos/plugins/jsc/raw/.claude-plugin/marketplace.json`. Clone any domain repo missing from the working directory (`gitea.sh clone-url plugins/{domain}`) and pull the rest. Completion condition: every domain repo exists locally and is current.
 2. Audit every skill of every domain against the guidelines.md audit checklist — this step MUST run as a sub agent, one sub agent per domain repo. Each sub agent reports its findings: skill, failed checklist item, evidence (file:line), proposed fix. Completion condition: every domain has an audit result.
 3. Present each failed item via the `jsc-ask:ask` decision tree (apply the proposed fix / skip / custom fix). Every option states its impact scope (example: skipping leaves the skill non-compliant until the next audit). Completion condition: every finding has a recorded decision.
-4. Apply the confirmed fixes — this step MUST run as a sub agent, one sub agent per affected domain repo: modify the files, sync that domain README's 「Skills 目錄」 section, and bump the version in all three manifests. Completion condition: every affected repo carries the fixes and the manifest bump.
+4. Apply the confirmed fixes — the fix-application part MUST run as a sub agent, one sub agent per affected domain repo: modify the files per the confirmed fix. Then run `tools/sync-skill-manifest.sh {domain-path}` directly (no sub agent needed) for each affected domain repo to refresh that domain README's 「Skills 目錄」 section and bump the version in all three manifests. Completion condition: every affected repo carries the fixes and the manifest bump.
 5. Re-check the guidelines.md audit checklist for every touched skill. On any failure, **return to step 3**: confirm and fix again, until all items pass. Completion condition: all checklist items pass.
 6. Call `jsc-git:pr` once per affected domain repo to open a Push Request. Completion condition: every affected repo has a PR URL.