Wraps git archive with --prefix=last30days/ so the zip contains a single
top-level skill folder matching SKILL.md's name: frontmatter. Enforces:
- refuses to build with a dirty working tree (prevents shipping untracked changes)
- fails if zip exceeds 200 files (claude.ai's empirical upload cap)
- fails if zip contains more than one SKILL.md (avoids name: confusion)
Output at dist/last30days.skill (gitignored).
Matt Van Horn
039fc89874