feat(phone-image): 增加翻页预览与无封面图排版样式

- 为手机截图生成器添加翻页功能，支持在生成前预览各页内容
- 增加无封面图时的排版样式，使用装饰线条和居中布局
- 改进图片处理逻辑，清除内联样式并展平嵌套包装元素
- 修复 models.dev 同步接口，支持 GET 请求获取缓存数据
- 优化网络请求，添加直连失败后的本地代理重试机制

public/static/css/phone-image-templates.css

@@ -116,6 +116,80 @@
     margin-top: var(--pi-spacing-sm);
 }
 
+/* --- 封面页 - 无封面图装饰排版 --- */
+.page-cover.no-cover-image {
+    justify-content: center;
+    padding: var(--pi-spacing-lg);
+}
+
+.page-cover.no-cover-image .cover-decor-line {
+    position: absolute;
+    left: 30px;
+    right: 30px;
+    height: 2px;
+    background: var(--pi-color-border);
+}
+
+.page-cover.no-cover-image .cover-decor-top {
+    top: 80px;
+}
+
+.page-cover.no-cover-image .cover-decor-bottom {
+    bottom: 80px;
+}
+
+.page-cover.no-cover-image .cover-no-img-content {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    text-align: center;
+    padding: var(--pi-spacing) 0;
+}
+
+.page-cover.no-cover-image .cover-no-img-title {
+    font-size: 36px;
+    font-weight: bold;
+    line-height: 1.4;
+    color: var(--pi-color-text);
+    word-break: break-word;
+    margin-bottom: var(--pi-spacing);
+    padding: 0 20px;
+}
+
+.page-cover.no-cover-image .cover-decor-divider {
+    width: 60px;
+    height: 3px;
+    background: var(--pi-color-accent);
+    margin-bottom: var(--pi-spacing);
+}
+
+.page-cover.no-cover-image .cover-no-img-desc {
+    font-size: var(--pi-font-size-subtitle);
+    color: var(--pi-color-text-light);
+    line-height: 1.8;
+    margin-bottom: var(--pi-spacing);
+    padding: 0 30px;
+    word-break: break-word;
+}
+
+.page-cover.no-cover-image .cover-no-img-meta {
+    display: flex;
+    gap: 15px;
+    font-size: var(--pi-font-size-small);
+    color: var(--pi-color-text-lighter);
+    flex-wrap: wrap;
+    justify-content: center;
+}
+
+/* --- 内容页图片强制约束 --- */
+.page-content img {
+    max-width: 100% !important;
+    height: auto !important;
+    display: block;
+    margin: 10px 0;
+}
+
 /* --- 内容页 --- */
 .page-body {
     display: flex;
@@ -170,6 +244,28 @@
     margin-bottom: var(--pi-spacing-sm);
 }
 
+.page-content h4 {
+    font-size: var(--pi-font-size-base);
+    font-weight: bold;
+    margin-top: var(--pi-spacing-sm);
+    margin-bottom: 5px;
+}
+
+.page-content h5 {
+    font-size: 13px;
+    font-weight: bold;
+    margin-top: var(--pi-spacing-sm);
+    margin-bottom: 5px;
+}
+
+.page-content h6 {
+    font-size: 12px;
+    font-weight: bold;
+    margin-top: var(--pi-spacing-sm);
+    margin-bottom: 5px;
+    color: var(--pi-color-text-light);
+}
+
 .page-content blockquote {
     border-left: 3px solid var(--pi-color-accent);
     padding-left: var(--pi-spacing-sm);