docs(graceful-handoff): align README with marketplace standard
Plugin README rewritten from 187 to 354 lines in the same shape as
ai-psychosis, llm-security, config-audit, and ms-ai-architect:
- English (other plugin READMEs are English)
- Standard solo-project + AI-generated disclaimers
- Badges row (version, platform, skill/hooks/pipeline counts, tests, license)
- Table of Contents
- Mermaid architecture diagram (detection / pipeline / resumption / manual)
- 4-step context resolution table (v2.1)
- Components section (skill, pipeline, hooks)
- Workflow examples + safety guarantees + limitations
- Inline version history + Feedback & Contributing
Root README graceful-handoff card updated to reflect v2.1 model-aware
detection and 57-test count (was 36).