docs: clarify plugin setup and runtime

[cablate]

Summary

• lead with a clear choice between Codex Plugin, MCP stdio, and Streamable HTTP
• document runtime Skill loading, prerequisites, local doctor checks, and billable live diagnostics
• align English and Traditional Chinese onboarding and expand the no-MCP demo
• refine public plugin metadata and prepare v0.0.66

Validation

• python scripts/validate-skills.py
• npm run test:unit (36 passed)
• npm test (114 passed)
• npm run lint (0 errors; existing warnings)
• npm run build
• npm pack --dry-run
• local Markdown link check
• Skill Lens: OpenAI plugin contract passed; NVIDIA Tier 1 passed for all 3 Skills; Tier 2 similarity retained for human review