docs: Add CLAUDE.md with project development guidelines

[hristoterezov]

Summary

Adds CLAUDE.md to provide context and guidelines for Claude Code (AI-assisted development) when working on this repository. This documentation helps AI assistants understand the project structure, conventions, and workflows.

Changes

• Added CLAUDE.md with comprehensive project documentation

Content Overview

The CLAUDE.md file includes:

Project Information

• Overview of @jitsi/js-utils as a collection of utility libraries
• Package publishing details (npm, ES6 modules)
• Entry point and module structure

Development Workflow

• Build commands (npm run build, npm run gen-types)
• Linting configuration (@jitsi/eslint-config)
• Pre-commit hooks setup

Code Architecture

• Module-by-module breakdown of the codebase
• Key features and patterns for each utility (avatar, browser-detection, jitsi-local-storage, transport, etc.)
• Dependency information

Coding Conventions

• JSDoc requirements for all exports
• TypeScript preferences and migration guidance
• Naming conventions (UPPER_CASE for constants, underscore for private members)
• Event emitter patterns

TypeScript Configuration

• Target ES6 modules with strict mode
• Declaration file generation process
• Gradual migration strategy

Benefits

• 🤖 Improves AI-assisted development quality and consistency
• 📚 Provides quick reference for project structure and conventions
• 🎯 Helps maintain coding standards across AI-generated contributions
• 🔄 Documents TypeScript migration strategy
• 📖 Serves as onboarding documentation for both humans and AI

Notes

This file is specifically formatted for Claude Code but is also useful as general project documentation.