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

f_core/polyfill.php

@@ -0,0 +1,38 @@
+<?php
+defined('_ISVALID') or header('Location: /error');
+
+// Minimal polyfills for PHP 8.1+ removals used in this codebase
+
+if (!function_exists('strftime')) {
+    function strftime($format, $timestamp = null)
+    {
+        $timestamp = $timestamp ?? time();
+        // Map common strftime tokens to date() tokens
+        $replacements = [
+            '%a' => 'D',      // abbreviated weekday name
+            '%A' => 'l',      // full weekday name
+            '%d' => 'd',      // day of month, zero-padded
+            '%e' => 'j',      // day of month, no leading zero
+            '%u' => 'N',      // ISO-8601 numeric day of week (1-7)
+            '%w' => 'w',      // numeric day of week (0-6)
+            '%b' => 'M',      // abbreviated month name
+            '%B' => 'F',      // full month name
+            '%m' => 'm',      // month (01-12)
+            '%y' => 'y',      // 2-digit year
+            '%Y' => 'Y',      // 4-digit year
+            '%H' => 'H',      // hour 00-23
+            '%I' => 'h',      // hour 01-12
+            '%M' => 'i',      // minute 00-59
+            '%S' => 's',      // second 00-59
+            '%T' => 'H:i:s',  // time
+            '%p' => 'A',      // AM/PM
+            '%P' => 'a',      // am/pm
+            '%z' => 'O',      // GMT offset
+            '%Z' => 'T',      // timezone abbreviation
+            '%%' => '%',      // literal percent
+        ];
+        $phpFormat = strtr($format, $replacements);
+        return date($phpFormat, is_numeric($timestamp) ? (int) $timestamp : strtotime((string) $timestamp));
+    }
+}
+