feat(scys): add SCYS browser adapters

[warkcod]

Summary

• add SCYS browser adapters for course, toc, read, feed, opportunity, activity, and article extraction
• add shared SCYS extraction, course image download, and normalization helpers with adapter test coverage
• add SCYS adapter docs, schema guidance, and regenerate the CLI manifest

Test Plan

• npm run build
• npm run typecheck
• npm test
• npx vitest run --project adapter
• bash scripts/check-doc-coverage.sh --strict

[Astro-Han]

There is a lot of work here, and the adapter itself looks substantial. My only review note is about deliverables around discoverability.

From what I can tell, the PR adds the SCYS adapter page and the adapters index entry, but not the other repo-level updates that usually ship with a new adapter, namely the VitePress sidebar and the command tables in README.md and README.zh-CN.md. I think it would be worth adding those before merge so the new adapter is discoverable from the main docs and README surfaces.