skill-creator: drop ANTHROPIC_API_KEY requirement from description optimizer (#547)

improve_description.py now calls `claude -p`
as a subprocess instead of the Anthropic SDK, so users no longer need a
separate ANTHROPIC_API_KEY to run the description optimization loop. Same
auth pattern run_eval.py already used for the triggering eval.

Prompts go over stdin (they embed the full SKILL.md body). Strips CLAUDECODE
env var to allow nesting inside a Claude Code session. The over-1024-char
retry is now a fresh single-turn call that inlines the too-long version
rather than a multi-turn followup.

SKILL.md: dropped the stale "extended thinking" reference to match.

skills/skill-creator/scripts/run_loop.py

@@ -15,8 +15,6 @@ import time
 import webbrowser
 from pathlib import Path
 
-import anthropic
-
 from scripts.generate_report import generate_html
 from scripts.improve_description import improve_description
 from scripts.run_eval import find_project_root, run_eval
@@ -75,7 +73,6 @@ def run_loop(
         train_set = eval_set
         test_set = []
 
-    client = anthropic.Anthropic()
     history = []
     exit_reason = "unknown"
 
@@ -200,7 +197,6 @@ def run_loop(
             for h in history
         ]
         new_description = improve_description(
-            client=client,
             skill_name=name,
             skill_content=content,
             current_description=current_description,