fix: configure Element Plus Chinese locale (zh-cn)

Add zh-cn locale to Element Plus globally via app.use() and el-config-provider wrapper, and apply :locale prop to all el-date-picker components in dialogs to ensure correct Chinese display in date pickers, calendars, and other locale-aware UI.

Made-with: Cursor

WebUI/src/App.vue

@@ -6,6 +6,7 @@ import { useCategoryStore } from '@/stores/useCategoryStore'
 import { useTagStore } from '@/stores/useTagStore'
 import { useUIStore } from '@/stores/useUIStore'
 import { useUserSettingsStore } from '@/stores/useUserSettingsStore'
+import zhCn from 'element-plus/es/locale/lang/zh-cn'
 import AppHeader from '@/components/AppHeader.vue'
 import TaskDialog from '@/components/TaskDialog.vue'
 import CategoryDialog from '@/components/CategoryDialog.vue'
@@ -60,6 +61,7 @@ onMounted(async () => {
 </script>
 
 <template>
+  <el-config-provider :locale="zhCn">
   <div class="app-container">
     <div class="decoration-star" style="top: 20%; right: 8%; animation-delay: 0.5s;"></div>
     <div class="decoration-star" style="top: 60%; left: 3%; animation-delay: 1s;"></div>
@@ -97,6 +99,7 @@ onMounted(async () => {
     <TaskDialog />
     <CategoryDialog />
   </div>
+  </el-config-provider>
 </template>
 
 <style scoped lang="scss">