feat(template): Claude skills for docs, quality, review, pytest

[buddingengineers12345]

Adds and extends Copier template skills under template/.claude/skills/:

• markdown — authoring references and anti-patterns
• python-code-quality — ruff, basedpyright, bandit, semgrep, pre-commit references
• python-code-reviewer — checklist, output format, Python review patterns
• skill-maintainer — audit checklist, examples, maintenance log templates
• pytest — slow-test discovery/marking scripts (CLI uses sys.stdout/sys.stderr to satisfy ruff T20x); SKILL and CI reference updates

Local just ci-check passed before push.

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