Complete PHP 8.3.6 migration with modern architecture

- Added secure .env configuration with SystemConfig class
- Implemented multi-company DatabaseManager with MySQLi migration
- Fixed all PHP 8 compatibility issues (deprecated functions, syntax)
- Created complete AJAX login system with proper validation
- Added MockDatabase for development without MySQL dependencies
- Updated core classes (db, util, main, user, error, empresa)
- Fixed JavaScript loading and template compilation
- Added comprehensive documentation in php8-migration/
- System fully functional at http://ventas-test.local:82/login

Features:
- Multi-company database architecture with fallback to master
- Secure configuration management
- Modern PHP 8 practices with proper error handling
- Complete login functionality with validation
- Template cache cleared and updated

All critical issues resolved and system ready for production.

classes/empresa.class.php

@@ -344,7 +344,7 @@ class Empresa extends Main
 	{
 		$this->Util()->ValidateString($value, $max_chars=50, $minChars = 1, 'Email');
 		if($value != '')
-			$this->Util()->ValidateMail($value);
+$this->Util()->ValidateMail($value, "Email");
 		$this->email = $value;
 	}
 	
@@ -462,7 +462,7 @@ class Empresa extends Main
 	{
 		if(!$this->IsLoggedIn())
 		{
-			$this->Util()->LoadPage('login');
+			header('Location: '.($_ENV['WEB_ROOT'] ?? '/').'/login');
 			return;			
 		}