优化开发服务器静态资源加载：router.php 注入缓存头

为 JS/CSS/图片/字体等静态资源添加 ETag、Last-Modified、Cache-Control 响应头，
支持 304 Not Modified，避免浏览器每次完整重新下载。其余文件走原有逻辑。

public/router.php

@@ -1,7 +1,76 @@
 <?php
 // $Id$
 
-if (is_file($_SERVER["DOCUMENT_ROOT"] . $_SERVER["SCRIPT_NAME"])) {
+$uri  = parse_url($_SERVER["REQUEST_URI"], PHP_URL_PATH);
+$file = $_SERVER["DOCUMENT_ROOT"] . $uri;
+
+if (is_file($file)) {
+    $ext = strtolower(pathinfo($file, PATHINFO_EXTENSION));
+
+    // 仅对真正的静态资源注入缓存头，其余走原逻辑
+    $cacheExts = [
+        'js', 'css', 'png', 'jpg', 'jpeg', 'gif', 'svg', 'ico', 'webp',
+        'woff', 'woff2', 'ttf', 'eot', 'otf', 'map',
+        'json', 'xml', 'pdf', 'zip', 'mp3', 'mp4', 'wav', 'avi',
+    ];
+
+    if (in_array($ext, $cacheExts)) {
+        $realPath = realpath($file);
+        $docRoot  = realpath($_SERVER["DOCUMENT_ROOT"]);
+
+        // 路径穿越防护
+        if ($realPath === false || !str_starts_with($realPath, $docRoot)) {
+            http_response_code(403);
+            exit;
+        }
+
+        $etag = '"' . filemtime($file) . '-' . filesize($file) . '"';
+
+        // 304 Not Modified
+        if (
+            (isset($_SERVER['HTTP_IF_NONE_MATCH']) && $_SERVER['HTTP_IF_NONE_MATCH'] === $etag) ||
+            (isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) >= filemtime($file))
+        ) {
+            http_response_code(304);
+            exit;
+        }
+
+        header('ETag: ' . $etag);
+        header('Last-Modified: ' . gmdate('D, d M Y H:i:s', filemtime($file)) . ' GMT');
+        header('Cache-Control: public, max-age=86400');
+        header('X-Content-Type-Options: nosniff');
+
+        $mimeMap = [
+            'js'   => 'application/javascript',
+            'css'  => 'text/css',
+            'png'  => 'image/png',
+            'jpg'  => 'image/jpeg',
+            'jpeg' => 'image/jpeg',
+            'gif'  => 'image/gif',
+            'svg'  => 'image/svg+xml',
+            'ico'  => 'image/x-icon',
+            'webp' => 'image/webp',
+            'woff'  => 'font/woff',
+            'woff2' => 'font/woff2',
+            'ttf'   => 'font/ttf',
+            'eot'   => 'application/vnd.ms-fontobject',
+            'otf'   => 'font/otf',
+            'map'   => 'application/json',
+            'json'  => 'application/json',
+            'xml'   => 'application/xml',
+            'pdf'   => 'application/pdf',
+            'zip'   => 'application/zip',
+            'mp3'   => 'audio/mpeg',
+            'mp4'   => 'video/mp4',
+            'wav'   => 'audio/wav',
+            'avi'   => 'video/x-msvideo',
+        ];
+        header('Content-Type: ' . ($mimeMap[$ext] ?? 'application/octet-stream'));
+        readfile($file);
+        exit;
+    }
+
+    // PHP、HTML 等文件交给 PHP 内置服务器处理
     return false;
 } else {
     require __DIR__ . "/index.php";