chore: 添加缺失的静态资源文件

添加多个前端界面所需的图片、字体、音频等静态资源文件，包括：
- 管理员后台的图标、背景图、组件图片
- 移动端页面的商品图片、用户中心图片、活动图标
- 第三方库的示例图片和字体文件
- 浏览器兼容性配置文件
- 图标字体文件（eot、ttf、woff、woff2格式）

这些资源是前端界面正常显示所必需的，之前可能因版本控制忽略或遗漏而缺失。

vendor/symfony/mime/Encoder/Base64Encoder.php

@@ -0,0 +1,41 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Mime\Encoder;
+
+/**
+ * @author Chris Corbyn
+ */
+class Base64Encoder implements EncoderInterface
+{
+    /**
+     * Takes an unencoded string and produces a Base64 encoded string from it.
+     *
+     * Base64 encoded strings have a maximum line length of 76 characters.
+     * If the first line needs to be shorter, indicate the difference with
+     * $firstLineOffset.
+     */
+    public function encodeString(string $string, ?string $charset = 'utf-8', int $firstLineOffset = 0, int $maxLineLength = 0): string
+    {
+        if (0 >= $maxLineLength || 76 < $maxLineLength) {
+            $maxLineLength = 76;
+        }
+
+        $encodedString = base64_encode($string);
+        $firstLine = '';
+        if (0 !== $firstLineOffset) {
+            $firstLine = substr($encodedString, 0, $maxLineLength - $firstLineOffset)."\r\n";
+            $encodedString = substr($encodedString, $maxLineLength - $firstLineOffset);
+        }
+
+        return $firstLine.trim(chunk_split($encodedString, $maxLineLength, "\r\n"));
+    }
+}