feat: Add comprehensive documentation suite and reorganize project structure

- Created complete documentation in docs/ directory
- Added PROJECT_OVERVIEW.md with feature highlights and getting started guide
- Added ARCHITECTURE.md with system design and technical details
- Added SECURITY.md with comprehensive security implementation guide
- Added DEVELOPMENT.md with development workflows and best practices
- Added DEPLOYMENT.md with production deployment instructions
- Added API.md with complete REST API documentation
- Added CONTRIBUTING.md with contribution guidelines
- Added CHANGELOG.md with version history and migration notes
- Reorganized all documentation files into docs/ directory for better organization
- Updated README.md with proper documentation links and quick navigation
- Enhanced project structure with professional documentation standards

tests/preflight.php

@@ -0,0 +1,14 @@
+<?php
+// Simple preflight/health endpoint
+define('_ISVALID', true);
+include_once __DIR__ . '/../f_core/config.core.php';
+
+header('Content-Type: application/json');
+
+$status = [
+    'status' => 'ok',
+    'time' => date('c'),
+    'db' => isset($class_database) ? 'connected' : 'unavailable',
+];
+
+echo json_encode($status);