refactor(skills)!: rename kvb-git-changelog to kvb-release-changelog

A new release category groups what announces a release (changelog,
article, posts); the changelog skill is its first member. The naming
test lists the category and the README organigram places the skill
under it.

BREAKING CHANGE: /kvb-git-changelog is now /kvb-release-changelog;
make install replaces the installed copy, kvb-skill-cleanup removes the
legacy directory.

Evidence: make test green, ruff and markdownlint clean
(/tmp/rename-changelog-make-test-2.log); no reference to the old name
left in the tree; MEDUSA 5 files, 0 findings.

🎯 Fix: 97 %
💥 Break: 3 %
💸 Cost: 100 %
⏱️ Time: –
🛡️ Security: 100 %
🏆 Score: 94
🚦 Gate: ✅ 90/5, cost and time <= 100, security 100 %

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_naming.py

@@ -9,7 +9,7 @@ from pathlib import Path
 REPO_ROOT = Path(__file__).resolve().parents[1]
 SKILLS = REPO_ROOT / "skills"
 README = REPO_ROOT / "README.md"
-CATEGORIES = ("think", "create", "code", "ci", "git", "check", "org", "agent", "skill", "coach")
+CATEGORIES = ("think", "create", "code", "ci", "git", "release", "check", "org", "agent", "skill", "coach")
 UNCATEGORIZED = frozenset(
     {
         "kvb-cleanup",