docs: clarify README features and onboarding flow

[jwx0925]

Summary

The README makes readers navigate installation details before reaching the first sandbox workflow, and its feature and example lists are difficult to scan. Clarify the opening, add direct navigation, and organize capabilities and use cases into tables.

• Highlight Fast Sandbox on Kubernetes with reference warm end-to-end creation results: 97 ms P50 for serial requests and 308 ms P99 at 10-way concurrency. Link the measurement conditions and Firecracker pause/resume documentation.
• Put Getting Started and Examples directly after Features; retain the existing Quick Start code and installation instructions.
• Simplify credential and SDK descriptions, move the registry section after the client tools, and consolidate documentation and roadmap links.

Testing

• Manual verification: table structure, all local Markdown link targets, and section anchors
• Confirmed Quick Start, SDK installation, CLI, MCP, and registry content remained unchanged while moving sections
• git diff --check
• cd docs && pnpm docs:build (passed; bundle-size warning only)
• Unit, integration, and e2e suites not run: README-only change. Performance figures were checked against the existing report; benchmarks were not rerun.

Breaking Changes

• None

Checklist

• Linked Issue or clearly described motivation
• Added/updated docs (if needed)
• Added/updated tests (if needed): not applicable to README-only edits
• Security impact considered
• Backward compatibility considered

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	⚠️ Failed 2026-09-30T04:04:47.264600Z	a6514a7	PR opened

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review" or "@codex security review".

Codex reacts with 👀 while any review is running, comments if it has suggestions, and reacts with 👍 once all reviews finish with no findings.