docs: add architecture diagram and explanation

[POWDER-RANGER]

Description

Adds a comprehensive system architecture document with detailed Mermaid diagrams and explanations as requested.

Type of Change

• Documentation update

Changes Made

• Complete architecture diagram: Added comprehensive Mermaid flowchart showing all system components
• Frontend Layer: TypeScript/React components with port mappings and critical paths
• Backend Layer: Node.js/Express API services (User, Data, Report, Notification services)
• ML Layer: Python/TensorFlow ML Engine with NLP and Analytics capabilities
• Database Layer: PostgreSQL primary database with Redis cache and Object Storage
• Data Flow Architecture: Detailed async communication patterns and processing flows
• Health Check Flow: Application health monitoring with endpoint specifications
• Critical Paths: User authentication, data processing, and report generation paths
• API Endpoint Summary: Complete REST API endpoint documentation
• Security Architecture: Authentication, data security, and infrastructure security
• Performance Considerations: Caching, scalability, and optimization strategies

Key Features Added

• Visual Mermaid diagrams for system architecture and health checks
• Annotated async calls and webhook processing
• Health check flow with HTTP/TCP probes
• Critical path documentation for key user workflows
• Comprehensive API endpoint summary with all CRUD operations
• Technology stack details for each layer
• Port mappings and service connections
• Security and performance considerations

Testing

• Mermaid diagram syntax verified
• Markdown formatting validated
• All sections completed as requested

Additional Notes

This architecture document provides the detailed technical blueprint requested, including:

• Frontend (TypeScript/React) → Backend (Node/Express/API) → ML (Python/TensorFlow) → DB (Postgres) flow
• Embedded Mermaid diagrams for visual clarity
• Comprehensive endpoint summary and critical path documentation
• Production-ready architecture specifications