fix: 全站时间统一为北京时间(Asia/Shanghai)

新增 src/utils/datetime.ts 共享 formatBjTime 工具，
13 个页面(11后台+2前台) 的 toLocaleString/formatDate
改为显式北京时间。Dashboard.tsx 保留图表标签的
formatDate(split) 不受影响。

frontend/src/pages/front/EvolutionDashboard.tsx

@@ -4,6 +4,7 @@ import type { EvolutionSkill, EvolutionEvent, EvolutionProfile, SkillTreeData, S
 import html2canvas from 'html2canvas';
 import jsPDF from 'jspdf';
 import './EvolutionDashboard.css';
+import { formatBjTime } from '@/utils/datetime';
 
 // ==================== SVG Icons ====================
 const Icon: React.FC<{ children: React.ReactNode; size?: number; className?: string }> = ({ children, size = 16, className }) => (
@@ -486,7 +487,7 @@ const TimelinePanel: React.FC<{
                 <p className="evo-timeline-desc">{event.description}</p>
                 <div className="evo-timeline-time">
                   <Icon size={12}><circle cx="12" cy="12" r="10"/><polyline points="12 6 12 12 16 14"/></Icon>
-                  {new Date(event.created_at).toLocaleString()}
+                  {formatBjTime(event.created_at)}
                 </div>
               </div>
             </div>