feat(token): add batch API for fetching token keys

Add new endpoint POST /api/token/batch/keys to fetch multiple
token keys in a single request, improving performance when
exporting or copying multiple tokens.

- Backend: Add GetTokenKeysBatch controller and GetTokenKeysByIds model
- Backend: Add route with CriticalRateLimit and DisableCache middleware
- Frontend: Add fetchTokenKeysBatch helper function
- Frontend: Update useTokensData to use batch API for token export

model/token.go

@@ -481,3 +481,11 @@ func BatchDeleteTokens(ids []int, userId int) (int, error) {
 
 	return len(tokens), nil
 }
+
+func GetTokenKeysByIds(ids []int, userId int) ([]Token, error) {
+	var tokens []Token
+	err := DB.Select("id", commonKeyCol).
+		Where("user_id = ? AND id IN (?)", userId, ids).
+		Find(&tokens).Error
+	return tokens, err
+}