fix: login persistence, username login, realtime refresh, group name uniqueness

- Fix cookie path to '/' for auth persistence across page refreshes
- Login field now accepts both username and email
- Add 30s polling for group list and team session status refresh
- Add group name uniqueness check before creation

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/api/pocketbase.ts

@@ -10,7 +10,7 @@ pb.authStore.loadFromCookie(document.cookie)
 
 // 保存认证状态到 cookie
 pb.authStore.onChange(() => {
-  document.cookie = pb.authStore.exportToCookie({ httpOnly: false })
+  document.cookie = pb.authStore.exportToCookie({ httpOnly: false, path: '/' })
 })
 
 // 获取当前用户