修复 /admin/h5/ 无法访问：显式资源映射不支持 welcome page

Spring 显式 ResourceHandler 不会自动解析目录下的 index.html。
通过 ViewControllerRegistry 添加 /h5 → forward:/h5/index.html 转发。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

car-wash-admin/src/main/java/com/kym/admin/config/WebcontextConfig.java

@@ -2,15 +2,18 @@ package com.kym.admin.config;
 
 import org.springframework.context.annotation.Configuration;
 import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
+import org.springframework.web.servlet.config.annotation.ViewControllerRegistry;
 import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
 
 @Configuration
 public class WebcontextConfig implements WebMvcConfigurer {
 
+    @Override
+    public void addViewControllers(ViewControllerRegistry registry) {
+        registry.addViewController("/h5").setViewName("forward:/h5/index.html");
+        registry.addViewController("/h5/").setViewName("forward:/h5/index.html");
+    }
 
-    /**
-     * 静态资源文件配置(前端工程)
-     */
     @Override
     public void addResourceHandlers(ResourceHandlerRegistry registry) {
         registry.addResourceHandler("/static/**").addResourceLocations("classpath:/static/");