Add comprehensive project documentation

[Copilot]

The project lacked documentation. Created complete technical and user documentation covering architecture, API, operations, and development.

Documentation Structure (9 files, 152KB)

Core Reference

• README.md - Project overview, tech stack, quick start
• DOCS_INDEX.md - Central navigation hub organized by audience

Operations

• INSTALLATION.md - System requirements, setup procedures, web server configs (Apache/Nginx)
• CONFIGURATION.md - Database, email, file upload, integration settings across environments
• INTEGRATIONS.md - Bitrix CRM, Savvion BPM, Google Sheets, WHMCS setup and troubleshooting

Technical

• ARCHITECTURE.md - System design, component architecture, database schema, request flows
• API_DOCUMENTATION.md - 8 REST endpoints with auth, request/response formats, code examples (PHP/JS/Python/cURL)
• DEVELOPMENT.md - Environment setup, coding standards, Git workflow, security practices

User

• USER_GUIDE.md - 14 user roles, 5 workflows, features by role, FAQ

Coverage

• Authentication: Token-based API auth, session management, role-based access (14 levels)
• Integrations: Complete setup guides for Bitrix (lead/task management), Savvion (workflow), Google Sheets (reporting), WHMCS (billing)
• Security: Documents legacy MD5 hashing, mysql_* deprecation, recommends PDO migration and bcrypt
• Architecture: Monolithic PHP structure, procedural design, 374KB functions file requiring refactoring

Example: API Endpoint Documentation

// Create verification request
POST /api_verify.php?action=create_check
Authorization: Bearer {token}

{
  "client_ref": "EMP-2026-001",
  "applicant_name": "John Doe",
  "check_type": "employment",
  "company_id": 87
}

All documentation organized by audience: end users, system administrators, developers, and API consumers.

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