fix(frontend): change time format to 12-hour with AM/PM

- Change time locale from zh-CN to en-US to properly display AM/PM
- Increase letter-spacing for better readability (0.08em → 0.12em)
- Update all time displays to use 12-hour format consistently

frontend/src/pages/chat/index.vue

@@ -230,7 +230,7 @@ function renderMarkdown(content: string) {
           <div class="jarvis-date-row">
             <div class="jarvis-date-meta">
               <div class="jarvis-month">{{ clientTime.toLocaleString('zh-CN', { month: 'long' }) }} {{ clientTime.getFullYear() }}</div>
-              <div class="jarvis-time">{{ clientTime.toLocaleTimeString('zh-CN', { hour12: false }) }}</div>
+              <div class="jarvis-time">{{ clientTime.toLocaleTimeString('en-US', { hour12: true }) }}</div>
             </div>
             <div class="jarvis-location">
               <div class="location-info">