Add comprehensive Software Requirements Specification documentation for EMR Backend System

[Copilot]

This PR adds a complete Software Requirements Specification (SRS) documentation suite for the EMR (Electronic Medical Record) Backend System designed for Cambodia's healthcare infrastructure. The documentation enables developers to build the entire Laravel 12 backend system without needing access to existing database migrations or reference materials.

What's Added

📋 SOFTWARE_REQUIREMENTS_SPECIFICATION.md (20,636 characters)

Complete technical specification covering:

• System architecture and Laravel 12 framework requirements
• Functional requirements for all healthcare modules (Patient Management, Clinical Workflow, Medication Management, etc.)
• Technical requirements including database schema, API endpoints, and authentication
• Cambodia-specific requirements (Khmer language support, administrative divisions, healthcare regulations)
• Security, performance, and implementation guidelines
• Detailed data models with business rules

🗄️ DATABASE_DESIGN.md (22,504 characters)

Comprehensive database design documentation with:

• Complete table specifications with SQL DDL for all entities
• Entity relationship diagrams and mapping descriptions
• Indexing strategies and performance optimization guidelines
• Data types, constraints, and validation rules
• Laravel migration implementation patterns
• Geographic data structure for Cambodia's administrative hierarchy (25 provinces, 162 districts, 1,652 communes, 14,073 villages)

🔌 API_SPECIFICATION.md (20,990 characters)

Detailed API documentation including:

• Complete REST endpoint specifications with request/response examples
• Laravel Sanctum authentication flows and token management
• Standardized request/response formats and error handling
• Data validation rules and business logic constraints
• Rate limiting and security measures
• Testing strategies and Postman collection guidance

🚀 IMPLEMENTATION_GUIDE.md (29,880 characters)

Step-by-step development guide featuring:

• Environment setup and Laravel 12 configuration
• Complete implementation steps with code examples
• Database migration and seeding strategies
• Testing frameworks with feature and unit test examples
• Production deployment procedures with Nginx and Supervisor configuration
• Troubleshooting guides and performance optimization tips

Key Features Documented

Master Data Management: Terminologies, concepts, and Cambodia's complete geographic hierarchy
Healthcare Facilities: Organizations, facilities, departments, rooms, and services
Patient Management: Demographics, addresses, identities, and patient cards with ULID support
Clinical Workflow: Visits, encounters, observations, and conditions with complete audit trails
Medication Management: Instructions, requests, and dispensing workflows
Service Management: Laboratory, imaging, and procedure request handling
Financial Management: Invoicing and billing systems
Staff Management: Practitioners with qualifications and role-based permissions

Technical Specifications

• Framework: Laravel 12 with PHP 8.2+
• Authentication: Laravel Sanctum with device-specific tokens
• Database: MySQL 8.0+/PostgreSQL 14+ with comprehensive indexing
• Caching: Redis for sessions and performance optimization
• Architecture: RESTful API with JSON communication and standardized response formats
• Security: Role-based access control, audit trails, and Cambodia healthcare compliance

The documentation totals 93,910 characters across 4 comprehensive documents, providing everything needed to implement a production-ready EMR system for Cambodia's healthcare infrastructure.

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