[FEATURE] skill-creator plugin: support OAuth auth for improve_description.py

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The skill-creator plugin's improve_description.py calls the Anthropic Messages API directly via the Python SDK (anthropic.Anthropic()), which requires ANTHROPIC_API_KEY. Claude Code authenticates via OAuth tokens, so the improve step fails with 401: OAuth authentication is currently not supported. The eval step works fine because it uses claude -p.

Proposed Solution

Either allow OAuth tokens on the Messages API, or have improve_description.py use claude -p (like run_eval.py already does) so it works with the same auth Claude Code already has.

Also: improve_description.py line 117 uses thinking.type: "enabled" which is deprecated for newer models — should be "adaptive".

Alternative Solutions

Users can get a separate API key from console.anthropic.com, but this adds friction and separate billing.

Priority

Medium - Would be very helpful

Feature Category

API and model interactions

Use Case Example

Running the skill-creator's trigger optimization loop (run_loop.py) for a family of 9 custom skills. The eval phase completes successfully using claude -p, but the improvement phase crashes because improve_description.py uses the SDK directly and can't authenticate with OAuth.

Additional Context

_No response_