feat(frontend): add i18n support and navigation

- Install vue-i18n and configure locales (zh/en)
- Add complete navigation bar with 5 items: Home, About, Submit, Status, Tool Guide
- Add language switcher (中文/EN) with localStorage persistence
- Create HomeView with hero section, features, and quick links
- Create AboutView with features and usage guide
- Create ToolInfoView explaining BtToxin_Shoter principles (no formulas, no Digger)
- Update TaskSubmitForm: single file upload, genome/protein toggle, tooltips
- Update TaskMonitorView: i18n, queue status display
- Add queue_position field to TaskStatusResponse type

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/main.ts

@@ -1,12 +1,35 @@
 import { createApp } from 'vue'
 import { createPinia } from 'pinia'
+import { createI18n } from 'vue-i18n'
+import ElementPlus from 'element-plus'
+import 'element-plus/dist/index.css'
 
 import App from './App.vue'
 import router from './router'
 
+// Import translation files
+import zh from './locales/zh.json'
+import en from './locales/en.json'
+
+// Create i18n instance
+const i18n = createI18n({
+  legacy: false, // Use Composition API
+  locale: localStorage.getItem('locale') || 'zh', // Get from localStorage or default to Chinese
+  fallbackLocale: 'zh',
+  messages: {
+    zh,
+    en
+  }
+})
+
 const app = createApp(App)
 
 app.use(createPinia())
 app.use(router)
+app.use(i18n)
+app.use(ElementPlus)
+
+// Make i18n available globally
+app.config.globalProperties.$t = i18n.global.t
 
 app.mount('#app')