feat: add BuildVersion component to App.vue

- Import BuildVersion component
- Add to template (top-right corner fixed)
- Visible on all views

Build version format: 20260725133504-gitHash
Shows in top-right corner with monospace font

src/App.vue

@@ -2,6 +2,7 @@
 import { onMounted, onUnmounted, ref, watch } from 'vue'
 import { useRouter } from 'vue-router'
 import AgentTip from './components/AgentTip.vue'
+import BuildVersion from './components/BuildVersion.vue'
 import { loadUserBehavior } from '@/stores/agentStore'
 import { useI18n } from 'vue-i18n'
 import { changeLanguage, getCurrentLanguage } from './locales'