Add package.json with ESLint and Prettier as dev dependencies

[k-sry]

Summary

This PR adds package.json with ESLint and Prettier as development dependencies, along with npm scripts for linting and formatting, and improved VSCode settings for better developer experience.

Changes

• ✅ Created package.json with ESLint, Prettier, and required dependencies
• ✅ Added npm scripts for common tasks:
  • npm run lint - Run ESLint
  • npm run lint:fix - Auto-fix ESLint issues
  • npm run format - Format with Prettier
  • npm run format:check - Check Prettier formatting
• ✅ Updated .vscode/settings.json with:
  • Format on save enabled
  • ESLint auto-fix on save
  • Prettier as default formatter
• ✅ Specified Node.js >= 18 and npm >= 9 requirements

Benefits

• 🎯 Ensures all contributors use the same linting and formatting tools
• 🚀 Makes it easier for new contributors to set up their development environment
• ✨ Improves code quality and consistency across the codebase
• 🔧 Enables automated checks in CI/CD pipelines (future enhancement)

Testing

• ✅ npm install - Successfully installed dependencies
• ✅ npm run lint - Runs without errors
• ✅ npm run format:check - Detects formatting differences in existing code (as expected)

Notes

• This PR does not reformat existing code to avoid massive diffs
• The tools will work for new code and future changes
• If maintainers want to format all existing code, that can be done in a separate PR

Related Issues

• Addresses the need mentioned in #6721 (Coding experience checklist)
• Related to #6440 (Potential additions to .vscode directory)

Checklist

• [x] Tested locally
• [x] npm scripts work correctly
• [x] VSCode integration works
• [x] No breaking changes to existing workflow

[k-sry]

(I'm Japanese, so I used AI to help with some of the English wording.)

[Samq64]

There are already GitHub actions for Prettier formatting and ESLint validation although that one currently does not not apply the changes automaticlly.

[WorldLanguages]

Closing this preventively, unless PR author proves they know what they know what Scratch is