chore: Update skills (#12063)

Author: KATO-Hiro

.claude/skills/milestone-check/instructions.md

@@ -33,7 +33,9 @@ Check the following in order — stop processing a user as soon as a reason to s
    - Not found → continue
 
 2. Check [issue #1185](https://github.com/KATO-Hiro/AtCoderClans/issues/1185)
-   — users tracked there likely have no blog → skip Steps 3–4
+   - `- [ ] username` (unchecked) → blog confirmed absent; skip Steps 3–4
+   - `- [x] username` (checked) → already listed in Clans; skip entirely
+   - Not found → continue to Step 3
 
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