feat: add douban-skill + enhance skill-creator with development methodology

New skill: douban-skill
- Full export of Douban (豆瓣) book/movie/music/game collections via Frodo API
- RSS incremental sync for daily updates
- Python stdlib only, zero dependencies, cross-platform (macOS/Windows/Linux)
- Documented 7 failed approaches (PoW anti-scraping) and why Frodo API is the only working solution
- Pre-flight user validation, KeyboardInterrupt handling, pagination bug fix

skill-creator enhancements:
- Add development methodology reference (8-phase process with prior art research,
  counter review, and real failure case studies)
- Sync upstream changes: improve_description.py now uses `claude -p` instead of
  Anthropic SDK (no ANTHROPIC_API_KEY needed), remove stale "extended thinking" ref
- Add "Updating an existing skill" guidance to Claude.ai and Cowork sections
- Restore test case heuristic guidance for objective vs subjective skills

README updates:
- Document fork advantages vs upstream with quality comparison table (65 vs 42)
- Bilingual (EN + ZH-CN) with consistent content

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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,