feat(message): add message encryption with batch decryption optimization

- Add encryption configuration with environment variable support
- Implement batch parallel decryption for improved query performance
- Integrate message encryptor via wire dependency injection
- Add explicit Decrypt() method for single message decryption
- Optimize AfterFind hook to defer decryption for batch processing

internal/repository/message_repo.go

@@ -131,6 +131,10 @@ func (r *MessageRepository) GetMessages(conversationID string, page, pageSize in
 		Order("seq DESC").
 		Find(&messages).Error
 
+	if err == nil && len(messages) > 0 {
+		model.BatchDecryptMessagesParallel(messages)
+	}
+
 	return messages, total, err
 }
 
@@ -141,6 +145,11 @@ func (r *MessageRepository) GetMessagesAfterSeq(conversationID string, afterSeq
 		Order("seq ASC").
 		Limit(limit).
 		Find(&messages).Error
+
+	if err == nil && len(messages) > 0 {
+		model.BatchDecryptMessagesParallel(messages)
+	}
+
 	return messages, err
 }
 
@@ -155,6 +164,11 @@ func (r *MessageRepository) GetMessagesBeforeSeq(conversationID string, beforeSe
 	for i, j := 0, len(messages)-1; i < j; i, j = i+1, j-1 {
 		messages[i], messages[j] = messages[j], messages[i]
 	}
+
+	if err == nil && len(messages) > 0 {
+		model.BatchDecryptMessagesParallel(messages)
+	}
+
 	return messages, err
 }
 
@@ -350,6 +364,8 @@ func (r *MessageRepository) GetMessageByID(messageID string) (*model.Message, er
 	if err != nil {
 		return nil, err
 	}
+	// 单条消息直接解密
+	_ = message.Decrypt()
 	return &message, nil
 }