docs: refine ecosystem and writing workflows

[hyochan]

Summary

• Model library-specific modules in the ecosystem diagram, reveal Onside from the Expo card, and link both its setup guide and official site.
• Remove the unused ecosystem image and retired cloud-workspace guidance.
• Add concise reader-first documentation rules, shorten recent release notes without dropping compatibility or safety constraints, and synchronize agent/Cursor guidance.
• Add the repository-local loop-review skill for the latest-main-to-clean-merge workflow.

Verification

• packages/docs: typecheck and production build
• Repository: audit:parity, audit:docs, audit:deprecations, audit:release-state
• Documentation audit fixtures: 45 passed
• scripts/agent: typecheck and 65 tests passed
• Skill validation: loop-review, generate-doc, openiap-workflows
• Browser: collapsed module cue, hover/focus expansion, Onside setup navigation, and official Onside link

A preview recording is attached in a PR comment.

[coderabbitai]

Walkthrough

This PR adds extensible library modules with Onside links, concise reader-first documentation rules, synchronized agent and Cursor guidance, streamlined release notes, and a reusable loop-review workflow.

The initial automated review found three wording-contract issues. All three were fixed in d794d80, independently rechecked, and resolved.

[hyochan]

Preview

ecosystem-onside-preview.mp4

Shows the collapsed module cue, hover expansion, and navigation to the Onside setup guide.

[coderabbitai]

Automated review through 8789ec9 found three actionable wording-contract issues. They were fixed in d794d80, verified locally and by an independent self-review, replied to, and resolved.