refactor(phone-image): 清理死代码、修复历史记录和媒体标签安全移除

T8: 删除estimateImageHeight/estimateTableHeight/showGeneratedThumbnails/switchSize/
    getConfig/getPages/renderContentFlow等未使用函数，exportLongImage添加render锁检查
T9: loadFromHistory恢复pageAlignments，font_size→fontSize命名统一(PHP+JS双向兼容)，
    修复历史加载时fontSize显示值bug
T10: preprocessContent移除iframe/video/svg/embed/object标签，
    封面图添加onerror处理

public/static/js/phone-image.js

@@ -227,6 +227,14 @@ var PhoneImageEngine = (function () {
         if (!html) return '';
         html = html.replace(/<script[^>]*>[\s\S]*?<\/script>/gi, '');
         html = html.replace(/<style[^>]*>[\s\S]*?<\/style>/gi, '');
+
+        // 移除不支持的媒体标签
+        html = html.replace(/<iframe[\s\S]*?<\/iframe>/gi, '[媒体内容]');
+        html = html.replace(/<video[\s\S]*?<\/video>/gi, '[媒体内容]');
+        html = html.replace(/<svg[\s\S]*?<\/svg>/gi, '');
+        html = html.replace(/<embed[^>]*>/gi, '');
+        html = html.replace(/<object[\s\S]*?<\/object>/gi, '');
+
         // 清除空段落
         html = html.replace(/<p[^>]*>\s*<\/p>/gi, '');
 
@@ -357,7 +365,6 @@ var PhoneImageEngine = (function () {
                         block.estimatedHeight = 0;
                         block.needsMeasurement = true;
                     }
-                    block.$img = $el;
                     break;
                 case 'ul':
                 case 'ol':
@@ -415,22 +422,6 @@ var PhoneImageEngine = (function () {
         return lines * hSize * 1.4 + 20; // heading行高1.4 + 20px上下间距
     }
 
-    /**
-     * 估算图片高度
-     * 默认按内容区宽度的60%估算
-     */
-    function estimateImageHeight($img) {
-        var w = parseInt($img.attr('width'), 10);
-        var h = parseInt($img.attr('height'), 10);
-        if (w > 0 && h > 0) {
-            // 按比例缩放到内容宽度
-            var ratio = getContentWidth() / w;
-            return Math.round(h * ratio) + 10;
-        }
-        // 无尺寸信息时默认300px
-        return 310;
-    }
-
     /**
      * 估算列表高度
      */
@@ -447,15 +438,6 @@ var PhoneImageEngine = (function () {
         return estimateTextHeight(text, config.fontSize) + 10;
     }
 
-    /**
-     * 估算表格高度 (已废弃 - DOM实测替代)
-     * @deprecated 使用 measureBlockHeights() 替代
-     */
-    function estimateTableHeight($table) {
-        // DOM实测将覆盖此值，返回0作为占位
-        return 0;
-    }
-
     // ===== 分页核心算法 =====
 
     /**
@@ -644,7 +626,7 @@ var PhoneImageEngine = (function () {
         html += '" style="width:' + sizeConfig.width + 'px;height:' + sizeConfig.height + 'px;">';
 
         if (hasCover) {
-            html += '<img class="cover-image" src="' + escapeHtml(postData.poster) + '" alt="">';
+            html += '<img class="cover-image" src="' + escapeHtml(postData.poster) + '" alt="" onerror="this.style.display=\'none\'">';
             html += '<div class="cover-title">' + escapeHtml(postData.title) + '</div>';
             if (postData.desc) {
                 html += '<div class="cover-subtitle">' + escapeHtml(postData.desc) + '</div>';
@@ -1409,34 +1391,6 @@ var PhoneImageEngine = (function () {
         return deferred.promise();
     }
 
-    /**
-     * 将生成的canvas数组显示为缩略图
-     * @param {Array} canvases canvas对象数组
-     * @param {string} containerSelector 容器选择器
-     */
-    function showGeneratedThumbnails(canvases, containerSelector) {
-        var $container = $(containerSelector);
-        $container.empty();
-
-        for (var i = 0; i < canvases.length; i++) {
-            var thumb = canvases[i].toDataURL('image/jpeg', 0.5);
-            var $item = $('<div class="phone-thumb-item" data-index="' + i + '">' +
-                '<img src="' + thumb + '" alt="第' + (i + 1) + '页">' +
-                '<span class="phone-thumb-page">' + (i + 1) + '</span>' +
-                '</div>');
-            $container.append($item);
-        }
-    }
-
-    // ===== 配置切换 =====
-
-    /**
-     * 切换尺寸
-     */
-    function switchSize(name) {
-        config.size = name;
-    }
-
     // ===== 逐页对齐 =====
 
     /**
@@ -1456,6 +1410,13 @@ var PhoneImageEngine = (function () {
      */
     function exportLongImage() {
         var deferred = $.Deferred();
+
+        if (render._locked) {
+            layer.msg('请等待渲染完成');
+            deferred.reject('rendering');
+            return deferred.promise();
+        }
+
         var $flow = $('#content-flow');
         if (!$flow.length) {
             deferred.reject('内容流容器不存在');
@@ -1511,20 +1472,6 @@ var PhoneImageEngine = (function () {
         return div.innerHTML;
     }
 
-    /**
-     * 获取当前配置
-     */
-    function getConfig() {
-        return $.extend({}, config);
-    }
-
-    /**
-     * 获取分页结果
-     */
-    function getPages() {
-        return pages.slice();
-    }
-
     // ===== 公开API =====
     return {
         init: init,
@@ -1532,12 +1479,7 @@ var PhoneImageEngine = (function () {
         generateImages: generateImages,
         saveImages: saveImages,
         saveConfig: saveConfig,
-        showGeneratedThumbnails: showGeneratedThumbnails,
-        switchSize: switchSize,
-        getConfig: getConfig,
-        getPages: getPages,
         setPageAlignment: setPageAlignment,
-        renderContentFlow: renderContentFlow,
         insertPageBreak: insertPageBreak,
         removePageBreak: removePageBreak,
         exportLongImage: exportLongImage