feat: 新增App图标搜索器增强版功能

引入完整的App图标搜索器增强版，包括前端页面、后端缓存系统、样式和脚本。主要功能包括实时搜索、多尺寸图标下载、图片预览、响应式设计和智能缓存机制。后端通过ImageCache类实现图片缓存，前端通过JavaScript优化搜索交互和图片加载体验。新增README.md提供详细的部署和开发指南。

cache/ImageCache.php

@@ -0,0 +1,32 @@
+<?php
+class ImageCache {
+    private $cacheDir;
+    private $cacheDuration = 604800; // 7天缓存
+
+    public function __construct() {
+        $this->cacheDir = __DIR__ . '/images/';
+        if (!file_exists($this->cacheDir)) {
+            mkdir($this->cacheDir, 0777, true);
+        }
+    }
+
+    public function getCachedImage($url) {
+        $cacheFile = $this->cacheDir . md5($url);
+        
+        if (file_exists($cacheFile) && (time() - filemtime($cacheFile) < $this->cacheDuration)) {
+            return file_get_contents($cacheFile);
+        }
+
+        $imageContent = file_get_contents($url);
+        if ($imageContent !== false) {
+            file_put_contents($cacheFile, $imageContent);
+            return $imageContent;
+        }
+        
+        return false;
+    }
+
+    public function getCacheUrl($url) {
+        return 'cache/image.php?url=' . urlencode($url);
+    }
+}

cache/image.php

@@ -0,0 +1,37 @@
+<?php
+require_once 'ImageCache.php';
+
+$url = isset($_GET['url']) ? $_GET['url'] : '';
+if (empty($url)) {
+    header("HTTP/1.0 404 Not Found");
+    exit;
+}
+
+$imageCache = new ImageCache();
+$image = $imageCache->getCachedImage($url);
+
+if ($image === false) {
+    header("HTTP/1.0 404 Not Found");
+    exit;
+}
+
+$extension = pathinfo(parse_url($url, PHP_URL_PATH), PATHINFO_EXTENSION);
+switch(strtolower($extension)) {
+    case 'jpg':
+    case 'jpeg':
+        header('Content-Type: image/jpeg');
+        break;
+    case 'png':
+        header('Content-Type: image/png');
+        break;
+    case 'gif':
+        header('Content-Type: image/gif');
+        break;
+    default:
+        header('Content-Type: image/jpeg');
+}
+
+header('Cache-Control: public, max-age=31536000');
+header('Expires: ' . gmdate('D, d M Y H:i:s \G\M\T', time() + 31536000));
+
+echo $image;