feat(狀態回報): 收尾寫一筆 skill-end 事件

現行紀錄只記「被叫用」，沒有成敗也沒有結束碼。跑完整輪的技能與開場就
中止的技能，在紀錄裡長得一模一樣。

start 由技能用量 hook 順手發，不必改技能文件。end 只能由技能自己在收尾
步驟寫——hook 接在技能工具呼叫上，而實際工作發生在之後的模型輪次，它在
原理上看不到成敗。有 start 沒有配對的 end，就是那一輪中止了。

status 五選一，每支技能各自寫明什麼情況選哪一個。找不到回報腳本就安靜
跳過，回報失敗一律不改變技能自己的結論。

skills/pkg-update/SKILL.md

@@ -64,3 +64,7 @@ Exit 4 and exit 5 are the two codes whose meaning depends on the tool, so read t
    Step 3 is done only when every ecosystem landed in exactly one of three end states: exit 0 on the first run; exit 0 on the single retry, with every suspect of that ecosystem carrying a written hold plus a comment naming its reason; or entered step 4.
 4. A real install, build or test failure reached this step → revert. Run `tools/git-guard.sh revert {project dir} --confirm-destructive`. The script re-proves the target is a git work tree before it runs anything destructive, restores every tracked file with `git checkout -- .`, removes this run's untracked files with `git clean -fd`, and verifies `git status --porcelain` prints nothing. Gitignored paths survive `-fd` on purpose: `node_modules`, `__pycache__`, `bin/` and `obj/` stay behind, so restoring install output is out of scope for this skill. Route the exit code per the table above. Step 4 is done only when the script exited 0; report the failing packages with an error summary after that.
 5. Success → report the update list (package, old version, new version), every package held at its old version by step 3 with the reason, and every skip with its reason, then hand off to `jsc-git:commit`. Step 5 is done when the hand-off is made and every package from step 1 appears exactly once, as an update, a hold or a skip.
+6. **Record how the run ended.** This is the closing step and it runs on all three endings — the success of step 5, the revert of step 4, and every stop route. Run `jsc-hooks/tools/report-status.sh skill-end jsc-pkg:pkg-update {status} {exit} "{detail}"`; the leading `jsc-hooks/` is the whole point — every other script this skill runs is its own `tools/{name}.sh`, and this one lives in a sibling plugin, so a bare `tools/` path would resolve to a file that is not there. What records a skill's start cannot see how it ended, so an ending that is never written reads afterwards as a run that was abandoned mid-way, and a reverted run looks the same as a clean one.
+   - `{status}` is one of five. `ok`: every package landed on its new version and build and test passed, with no hold and no skip. `degraded`: the run finished and part of it did not land — a package held at its old version by step 3 while build and test passed on the retry, or a package skipped for a missing registry entry or a missing version source file. That is `degraded` and never `failed`, because step 5 was reached and the hand-off to `jsc-git:commit` was made. `failed`: a real install, build or test failure that step 3's single retry did not clear, so step 4 reverted the working tree. `blocked`: `git-guard.sh check` refused the run because the tree was not clean or was not a git work tree, so nothing was ever written. `aborted`: the run stopped before it could do its work on a precondition that does not hold — the inventory listed zero packages, or the user could not name a build and test command at substep 1.3.
+   - Take `{exit}` from the tool that decided the ending — the `build-test.sh`, `install-deps.sh` or `git-guard.sh` code that routed the run — and otherwise use 0 for `ok` and 1 for every other status. `{detail}` is optional, one line, at most 200 characters: the counts of updated, held and skipped packages, or the failing tool with its code. Never put a build log or a package list of unbounded length there; the full lists belong in the report of step 5.
+   - Reporting never changes the run. A machine without `report-status.sh` skips this step in silence and keeps its step 5 result exactly as it stands; the script swallows its own write failures and always exits 0, so nothing here is worth routing on. Step 6 is done when the call was made, or the script was absent and the step was skipped without a word.