create-react-on-rails-app: Follow-ups from PR #2375

[justin808]

Follow-up items from PR #2375 (create-react-on-rails-app CLI Phase 1).

Validation improvements

• App name validation: Require names start with a letter (/^[a-zA-Z][a-zA-Z0-9_-]*$/) — names like 123app or -myapp will cause rails new to fail or behave poorly
• Minimum Rails version check: validateRails only checks presence, not version — Rails 5 or 6 would produce an incompatible app. Add minimum version check (e.g., Rails 6.1+ or 7.0+)

Code quality

• Unreachable else branch in buildGeneratorArgs: Since --ignore-warnings is always pushed, args.length > 0 is always true — simplify the ternary
• process.exit(1) in createApp prevents composability: Consider having createApp throw or return a result instead, so the CLI entry point handles the exit and the function is testable
• Add JSDoc on execLive/execLiveArgs: Document shell-injection contract — callers must ensure command is shell-safe
• rm -rf in clean script is not cross-platform: Use node -e "require('fs').rmSync('./lib',{recursive:true,force:true})" or rimraf for Windows compatibility

Testing

• Add validateAll success-case test: Current tests verify the failure path but don't assert allValid === true when all prerequisites pass
• End-to-end test: Create an actual app with npx create-react-on-rails-app test-app and verify it boots (marked incomplete in PR test plan)

Documentation

• Update proposal doc to match implementation: Listed dependencies (chalk ^5.0.0, ora, prompts) diverge from actual implementation (chalk ^4.1.2 for CJS, no ora/prompts)

Future phases (from PR description and issue #1637)

• Yarn support: Original issue Proposal for New CLI Tool: create-react-on-rails-app to Streamline Project Initialization #1637 requested yarn_classic and yarn_berry — only npm/pnpm supported in Phase 1
• Redux templates
• Tailwind CSS integration
• Rspack bundler support: --rspack flag is wired up but needs end-to-end testing
• React on Rails Pro (--pro flag)

Build pipeline

• Consider topological build: Root build script chains 4 sequential pnpm --filter ... run build calls — if packages are independent, pnpm -r run build would be simpler

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Ref: PR #2375, Issue #1637