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/stechstudio/backoff/tests/HelpersTest.php

@@ -0,0 +1,69 @@
+<?php
+namespace STS\Backoff;
+
+use PHPUnit\Framework\TestCase;
+use STS\Backoff\Strategies\ConstantStrategy;
+
+class HelpersTest extends TestCase
+{
+    public function testSuccessWithDefaults()
+    {
+        $result = backoff(function() {
+            return "success";
+        });
+
+        $this->assertEquals("success", $result);
+    }
+
+    public function testFailureWithDefaults()
+    {
+        $this->expectException(\Exception::class);
+        $this->expectExceptionMessage("failure");
+
+        backoff(function() {
+            throw new \Exception("failure");
+        }, 2);
+    }
+
+    public function testStrategy()
+    {
+        $start = microtime(true);
+
+        // We're going to run a test for 100 attempts, just to verify we were able to
+        // set our own strategy with a low sleep time.
+
+        try {
+            backoff(function() {
+                throw new \Exception("failure");
+            }, 100, new ConstantStrategy(1));
+        } catch(\Exception $e) {}
+
+        $end = microtime(true);
+
+        $elapsedMS = ($end - $start) * 1000;
+
+        // We expect that this took just a bit over the 100ms that we slept
+        $this->assertTrue($elapsedMS > 100 && $elapsedMS < 200);
+    }
+
+    public function testWaitCap()
+    {
+        $start = microtime(true);
+
+        // We're going to specify a really long sleep time, but with a short cap to override.
+
+        try {
+            backoff(function() {
+                throw new \Exception("failure");
+            }, 2, new ConstantStrategy(100000), 100);
+        } catch(\Exception $e) {}
+
+        $end = microtime(true);
+
+        $elapsedMS = ($end - $start) * 1000;
+
+        // We expect that this took just a bit over the 100ms that we slept
+        $this->assertTrue($elapsedMS > 90 && $elapsedMS < 150,
+            sprintf("Expected elapsedMS between 90 & 200, got: $elapsedMS\n"));
+    }
+}