feat(typesetting): 页面品牌标识 - 数据链路+渲染函数+分页修正

- Post.php: phoneImage()传递siteName/siteLogo到模板
- phone_image.html: postData增加siteName/siteLogo字段
- phone-image.js: 新增generateBrandHeader()+preloadBrandLogo()
- phone-image.js: 3个页面生成函数调用品牌头部
- phone-image.js: contentAreaHeight扣减BRAND_HEADER_HEIGHT(36px)
- logo预转base64规避html2canvas CORS，过滤默认头像

view/admin/post/phone_image.html

@@ -307,6 +307,8 @@
                 contentHtml: $('#post-content-html').html(),
                 poster: <?php echo json_encode($post->poster ?? ''); ?>,
                 authorName: <?php echo json_encode($post->author_name ?? ''); ?>,
+                siteName: <?php echo json_encode($siteName ?? ''); ?>,
+                siteLogo: <?php echo json_encode($siteLogo ?? ''); ?>,
                 createTime: <?php echo json_encode($post->create_time_text ?? ''); ?>,
                 categoryName: ''
             };