fix(phone-image): 修复XSS注入、正则兼容性、render锁稳定性和缓存清理

T1: XSS修复 - PHP模板注入改用json_encode，poster URL转义处理
T2: fontSize NaN修复 - parseInt统一处理，lookbehind正则替换为兼容方案
T3: render锁稳定性 - insertPageBreak/removePageBreak添加15次重试上限，
     fontsReady添加catch处理，_pending递归添加错误捕获
T4: 缓存清理 - init()清空缓存，render()超过3倍blocks数自动清理

view/admin/post/phone_image.html

@@ -187,13 +187,13 @@
 
             var postData = {
                 postId: {$post.id},
-                title: '{$post.title|raw}',
-                desc: '{$post.desc|default=""}',
-                coverText: '{$post->getData("cover_text")|default=""}',
+                title: <?php echo json_encode($post->title ?? ''); ?>,
+                desc: <?php echo json_encode($post->desc ?? ''); ?>,
+                coverText: <?php echo json_encode($post->getData('cover_text') ?? ''); ?>,
                 contentHtml: $('#post-content-html').html(),
-                poster: '{$post.poster|default=""}',
-                authorName: '{$post.author_name|default=""}',
-                createTime: '{$post.create_time_text|default=""}',
+                poster: <?php echo json_encode($post->poster ?? ''); ?>,
+                authorName: <?php echo json_encode($post->author_name ?? ''); ?>,
+                createTime: <?php echo json_encode($post->create_time_text ?? ''); ?>,
                 categoryName: ''
             };