修复：Alpine.js userInfo.position_history 初始 undefined 导致 length 报错

- userInfo 初始值加 position_history: []，防止挂载时 undefined.length
- x-text 和 x-if 里加可选链 ?.length ?? 0 双重兜底

resources/views/chat/partials/user-actions.blade.php

@@ -77,7 +77,9 @@
     function userCardComponent() {
         return {
             showUserModal: false,
-            userInfo: {},
+            userInfo: {
+                position_history: []
+            },
             isMuting: false,
             muteDuration: 5,
             showWhispers: false,
@@ -490,7 +492,7 @@
                                cursor: pointer; font-size: 11px; font-weight: bold; color: #7c3aed;
                                margin-bottom: 4px; user-select: none;">
                         <span>🎖️ 职务履历 <span style="font-weight: normal; font-size: 10px; color: #9ca3af;"
-                                x-text="'（' + userInfo.position_history.length + ' 条）'"></span></span>
+                                x-text="'（' + (userInfo.position_history?.length ?? 0) + ' 条）'"></span></span>
                         <span x-text="showPositionHistory ? '▲' : '▼'" style="font-size: 10px; opacity:0.5;"></span>
                     </div>
                     {{-- 折叠内容 --}}
@@ -504,7 +506,7 @@
                                         :style="h.is_active ? 'background: #7c3aed; box-shadow: 0 0 0 3px #ede9fe;' :
                                             'background: #d1d5db;'">
                                     </div>
-                                    <template x-if="idx < userInfo.position_history.length - 1">
+                                    <template x-if="idx < (userInfo.position_history?.length ?? 0) - 1">
                                         <div style="width: 1px; flex: 1; background: #e5e7eb; margin-top: 2px;"></div>
                                     </template>
                                 </div>