feat(frontend): add weather icons and redesign calendar header

Backend changes:
- Add LOCATION configuration option to Settings
- Add /api/system/config endpoint to expose public config
- Implement location priority: config > geolocation > default

Frontend changes:
- Install and integrate weather-icons npm package (Erik Flowers)
- Redesign calendar header with date/time on left, weather/location on right
- Display weather icon using CSS classes instead of SVG components
- Fetch location from backend API on component mount
- Use configured location name (from .env) instead of geocoded result

Layout:
- Left: month/year + current time
- Right: city name + weather description + weather icon

frontend/src/pages/chat/index.vue

@@ -62,7 +62,7 @@ const {
 } = useKnowledgeView()
 
 // --- Client time & weather ---
-const { clientTime, weatherIcon, weatherSummary, formatClientDate, formatClientClock } = useClientTime()
+const { clientTime, city, weatherIcon, weatherSummary, formatClientDate, formatClientClock } = useClientTime()
 
 // --- Daily digest & reminders ---
 const { dailyDigest, digestLoading, activeReminder, reminderVisible, loadDailyDigest, handleSnooze, handleDismiss } = useDailyDigest()
@@ -228,11 +228,17 @@ function renderMarkdown(content: string) {
       <div v-else class="jarvis-sidebar-scroll">
         <div class="jarvis-panel jarvis-date-panel">
           <div class="jarvis-date-row">
-            <div class="jarvis-date-num">{{ clientTime.getDate().toString().padStart(2, '0') }}</div>
             <div class="jarvis-date-meta">
-              <div class="jarvis-month">{{ clientTime.toLocaleString('zh-CN', { month: 'long' }) }} / {{ clientTime.getFullYear() }}</div>
+              <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>
+            <div class="jarvis-location">
+              <div class="location-info">
+                <span class="location-name">{{ city }}</span>
+                <span class="location-weather-text">{{ weatherSummary }}</span>
+              </div>
+              <i :class="['wi', weatherIcon, 'location-icon']"></i>
+            </div>
           </div>
 
           <div class="jarvis-calendar">
@@ -564,7 +570,7 @@ function renderMarkdown(content: string) {
               <div class="runtime-meta-item">
                 <span class="runtime-meta-key">WEATHER</span>
                 <span class="runtime-meta-value weather-inline">
-                  <component :is="weatherIcon" :size="14" class="weather-icon" />
+                  <i :class="['wi', weatherIcon]"></i>
                   <span>{{ weatherSummary }}</span>
                 </span>
               </div>