refactor(component): 重构组件模板与样式结构

将公共样式提取至public.css，优化组件模板结构
添加图片资源与组件模板同步脚本
调整组件样式与布局，统一风格

js/sectionIndex.js

@@ -1,5 +1,5 @@
 const { createApp, ref, onMounted, nextTick, onUnmounted, computed, watch } = Vue;
-import { MyComponent } from "../component/item-forum/item-forum.js";
+import { itemForum } from "../component/item-forum/item-forum.js";
 
 const appSectionIndex = createApp({
     setup() {
@@ -8,5 +8,5 @@ const appSectionIndex = createApp({
         return { signInAlreadyState };
     },
 });
-appSectionIndex.component("MyComponent", MyComponent);
+appSectionIndex.component("item-forum", itemForum);
 appSectionIndex.mount("#sectionIndex");