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>

.gitignore

@@ -90,5 +90,5 @@ recovered_deep_research/
 # OpenCLI cache
 .opencli/
 
-# Work-in-progress skills
-douban-skill/
+# Eval workspaces (contain test data with personal info)
+douban-skill-workspace/