docs: add comprehensive architecture documentation for MCP Server

- Create ARCHITECTURE.md with detailed system design overview
- Describe key architectural components including Bun runtime, SSE communication, and modular design
- Highlight security, performance, and scalability features
- Outline future enhancement roadmap
- Provide insights into system design principles and technology choices

docs/ARCHITECTURE.md

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+# Architecture Documentation for MCP Server
+
+## Overview
+
+The MCP Server is designed as a high-performance, secure, and scalable bridge between Home Assistant and Language Learning Models (LLMs). This document outlines the architectural design principles, core components, and deployment strategies that power the MCP Server.
+
+## Key Architectural Components
+
+### High-Performance Runtime with Bun
+
+- **Fast Startup & Efficiency:** Powered by Bun, the MCP Server benefits from rapid startup times, efficient memory utilization, and native TypeScript support.
+- **Optimized Build Process:** Bun's build tools allow for quick iteration and deployment, ensuring minimal downtime and swift performance enhancement.
+
+### Real-time Communication using Server-Sent Events (SSE)
+
+- **Continuous Updates:** The server leverages SSE to deliver real-time notifications and updates, ensuring that any changes in Home Assistant are immediately communicated to connected clients.
+- **Scalable Connection Handling:** SSE provides an event-driven model that efficiently manages multiple simultaneous client connections.
+
+### Modular & Extensible Design
+
+- **Plugin Architecture:** Designed with modularity in mind, the MCP Server supports plugins, add-ons, and custom automation scripts, enabling seamless feature expansion without disrupting core functionality.
+- **Separation of Concerns:** Different components, such as device management, automation control, and system monitoring, are clearly separated, allowing independent development, testing, and scaling.
+
+### Secure API Integration
+
+- **Token-Based Authentication:** Robust token-based authentication mechanisms restrict access to authorized users and systems.
+- **Rate Limiting & Error Handling:** Integrated rate limiting combined with comprehensive error handling ensures system stability and prevents misuse.
+- **Best Practices:** All API endpoints follow industry-standard security guidelines to protect data and maintain system integrity.
+
+### Deployment & Scalability
+
+- **Containerized Deployment with Docker:** The use of Docker Compose enables straightforward deployment, management, and scaling of the server and its dependencies.
+- **Flexible Environment Configuration:** Environment variables and configuration files (.env) facilitate smooth transitions between development, testing, and production setups.
+
+## Future Enhancements
+
+- **Advanced Automation Logic:** Integration of more complex automation rules and conditional decision-making capabilities.
+- **Enhanced Security Measures:** Additional layers of security, such as multi-factor authentication and improved encryption techniques, are on the roadmap.
+- **Improved Monitoring & Analytics:** Future updates will introduce advanced performance metrics and real-time analytics to monitor system health and user interactions.
+
+## Conclusion
+
+The architecture of the MCP Server prioritizes performance, scalability, and security. By leveraging Bun's high-performance runtime, employing real-time communication through SSE, and maintaining a modular, secure design, the MCP Server provides a robust platform for integrating Home Assistant with modern LLM functionalities.
+
+*This document is a living document and will be updated as the system evolves.*