Add markdown file caching functionality

Add cache.php with get/set functions for markdown content Update
rendering to check cache before processing files

app/cache.php

@@ -0,0 +1,27 @@
+<?php
+
+function getCachedMarkdown(string $filePath): ?string {
+    $cacheDir = '/tmp/folderweb_cache';
+    $mtime = filemtime($filePath);
+    $cacheKey = md5($filePath . $mtime);
+    $cachePath = "$cacheDir/$cacheKey";
+    
+    if (file_exists($cachePath)) {
+        return file_get_contents($cachePath);
+    }
+    
+    return null;
+}
+
+function setCachedMarkdown(string $filePath, string $html): void {
+    $cacheDir = '/tmp/folderweb_cache';
+    if (!is_dir($cacheDir)) {
+        mkdir($cacheDir, 0755, true);
+    }
+    
+    $mtime = filemtime($filePath);
+    $cacheKey = md5($filePath . $mtime);
+    $cachePath = "$cacheDir/$cacheKey";
+    
+    file_put_contents($cachePath, $html);
+}

app/rendering.php

@@ -5,10 +5,19 @@ function renderContentFile(string $filePath): string {
     
     ob_start();
     if ($ext === 'md') {
+        require_once __DIR__ . '/cache.php';
+        $cached = getCachedMarkdown($filePath);
+        
+        if ($cached !== null) {
+            echo $cached;
+        } else {
             if (!class_exists('Parsedown')) {
                 require_once __DIR__ . '/vendor/Parsedown.php';
             }
-        echo '<article>' . (new Parsedown())->text(file_get_contents($filePath)) . '</article>';
+            $html = '<article>' . (new Parsedown())->text(file_get_contents($filePath)) . '</article>';
+            setCachedMarkdown($filePath, $html);
+            echo $html;
+        }
     } elseif (in_array($ext, ['html', 'php'])) {
         include $filePath;
     }