Docs: Add missing content pages (RSC landing, ExecJS, debugging, benchmarks)

[justin808]

Parent issue

Part of #2678 (Docs overhaul meta-issue)

Summary

Create new documentation pages that fill identified content gaps. These are net-new files — no restructuring or sidebar changes needed.

New pages to create (react_on_rails repo)

1. RSC Landing Page (docs/react-server-components/index.md)

• Top-level introduction to React Server Components support in React on Rails
• What RSC is, why it matters, current support status
• Links to tutorial, migration guide, and troubleshooting
• Clear note that RSC is a Pro feature

2. ExecJS Limitations (docs/core-concepts/execjs-limitations.md)

• Document known timer/async limitations (setTimeout, setInterval, promises)
• Explain why these fail in ExecJS vs Node.js rendering
• Common error messages and their causes
• Migration path to Node.js renderer (Pro)
• Partially addresses Documentation: ExecJS SSR Timer Limitations and Solutions #2299

3. Debugging Guide (docs/guides/debugging-react-on-rails.md or docs/building-features/debugging.md)

• Common debugging workflows for SSR issues
• How to inspect server-rendered HTML
• Using trace and logging configuration options
• Browser devtools tips for hydration mismatches
• Where to find relevant logs (Rails, Node, webpack)

4. Performance Benchmarks (docs/core-concepts/performance-benchmarks.md)

• SSR performance: ExecJS vs Node.js renderer
• Bundle splitting impact
• Streaming SSR benefits
• Before/after metrics from real deployments (reference testimonials)

Acceptance criteria

• Each page has clear, accurate content (not stubs)
• Pages follow existing doc style and formatting conventions
• Internal links to/from existing docs are added where relevant
• CI passes

Concurrency notes

• Fully concurrent with: Fix E2E test for Issue #2210 hydration mismatch #2679 (directory cleanup), Add documentation for custom Fastify configuration in node-renderer #2681 (sidebar rewrite), Document React on Rails 16.3.0 release in CHANGELOG #2682 (Pro interleaving)
• These are all new files with no overlap on existing content

🤖 Generated with Claude Code

[justin808]

Deep-dive triage pass (2026-03-22):

• Domain: documentation
• Labels/Priority signals: (none)
• Current PR coverage: open PR(s) already linked: Docs: Add RSC landing, ExecJS limitations, debugging, and benchmarks pages #2785
• Proposed next step: keep this issue paired to the current PR and focus on merge-blocker cleanup.

Question: Should this be batched with related docs issues in a single docs PR, or handled separately?