init command (SKILL.md template)

[johnnyhuy]

Summary

• Implement init command to scaffold SKILL.md.

Context

• Helps authors create compliant skills quickly.

Scope

• Create SKILL.md in current or specified directory.
• Validate name and avoid overwriting without confirmation.
• Populate a minimal AgentSkills template with required fields.

Out of scope

• Additional files (scripts/, references/) scaffolding.

Acceptance criteria

• init creates a valid SKILL.md and reports the path.
• Name validation prevents mismatches with directory name.