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/package.json

@@ -24,6 +24,7 @@
     "element-plus": "^2.13.0",
     "pinia": "^3.0.4",
     "vue": "^3.5.25",
+    "vue-i18n": "^9.14.2",
     "vue-router": "^4.6.3"
   },
   "devDependencies": {