Migrate skill versions from one Anthropic account to another

Copy one or more skill versions from a source Anthropic workspace into a destination workspace. Useful when you need to move custom skills off an account that is being deleted.

Flow (per {skill_id, version} entry):

1. GET /v1/skills/{skill_id}/versions/{version}/content using old_api_key → downloads a .zip archive containing SKILL.md and any extras.
2. The archive is parsed and the files (including SKILL.md) are re-uploaded to the destination account using new_api_key. Anthropic assigns a fresh skill_id in the new workspace.

Request body (JSON):

{
  "skills": [
    {"skill_id": "skill_017c48…", "version": "1759178010641129"},
    {"skill_id": "skill_01a7nM…", "version": "1761000123456789"}
  ],
  "old_api_key": "sk-ant-…",
  "new_api_key": "sk-ant-…"
}

oldApiKey / newApiKey (camelCase) are also accepted as aliases.

Existing endpoints (/claude/skills, /claude/skills/upload, etc.) are unaffected and continue to use the server-configured API key.