feat(settings): add home content customization and config injection

- Add home_content setting for custom homepage (HTML or iframe URL)
- Inject public settings into index.html to eliminate page flash
- Support ETag caching with automatic invalidation on settings update
- Add Vite plugin for dev mode settings injection
- Refactor HomeView to use appStore instead of local API calls

frontend/src/i18n/locales/en.ts

@@ -1828,7 +1828,10 @@ export default {
         logoHint: 'PNG, JPG, or SVG. Max 300KB. Recommended: 80x80px square image.',
         logoSizeError: 'Image size exceeds 300KB limit ({size}KB)',
         logoTypeError: 'Please select an image file',
-        logoReadError: 'Failed to read the image file'
+        logoReadError: 'Failed to read the image file',
+        homeContent: 'Home Page Content',
+        homeContentPlaceholder: 'Enter custom content for the home page. Supports Markdown & HTML. If a URL is entered, it will be displayed as an iframe.',
+        homeContentHint: 'Customize the home page content. Supports Markdown/HTML. If you enter a URL (starting with http:// or https://), it will be used as an iframe src to embed an external page. When set, the default status information will no longer be displayed.'
       },
       smtp: {
         title: 'SMTP Settings',

frontend/src/i18n/locales/zh.ts

@@ -1971,7 +1971,10 @@ export default {
         logoHint: 'PNG、JPG 或 SVG 格式，最大 300KB。建议：80x80px 正方形图片。',
         logoSizeError: '图片大小超过 300KB 限制（{size}KB）',
         logoTypeError: '请选择图片文件',
-        logoReadError: '读取图片文件失败'
+        logoReadError: '读取图片文件失败',
+        homeContent: '首页内容',
+        homeContentPlaceholder: '在此输入首页内容，支持 Markdown & HTML 代码。如果输入的是一个链接，则会使用该链接作为 iframe 的 src 属性。',
+        homeContentHint: '自定义首页内容，支持 Markdown/HTML。如果输入的是链接（以 http:// 或 https:// 开头），则会使用该链接作为 iframe 的 src 属性，这允许你设置任意网页作为首页。设置后首页的状态信息将不再显示。'
       },
       smtp: {
         title: 'SMTP 设置',