docs: Add comprehensive ARCHITECTURE.md documentation

[open-swe]

Fixes #29

Repository Architecture Documentation

This pull request adds a comprehensive ARCHITECTURE.md file to the repository, providing an in-depth overview of the Eternal project's architecture, technology stack, and design philosophy.

Key Documentation Sections

• Project Overview: Detailed description of Eternal as a node-based visual programming environment
• Technology Stack: Comprehensive breakdown of key dependencies and technologies
• Core Architecture Components: Deep dive into the node-based computation system
• Directory Structure: Detailed explanation of project organization
• Node System Architecture: Exploration of the plugin-based node system
• Development Workflow: Insights into build processes, type checking, and deployment
• Visual Programming Paradigm: Philosophical and practical foundations of the project

Documentation Highlights

• Covers 96+ node types across multiple domains
• Explains core architectural patterns (MVC, reactive programming)
• Details technology stack (React, Three.js, Tone.js, Redux, TensorFlow.js)
• Provides insights into the visual programming approach

The documentation aims to provide both new and experienced developers with a comprehensive understanding of the Eternal project's architecture and design principles.