feat: add MySQL database support with SQL translation

- Add MySQLConnection class with automatic SQL Server to MySQL translation
- Add connection factory to support both SQL Server and MySQL
- Update config schema to support MySQL configuration (host, port, db_type)
- Update default config to use MySQL (localhost:3306)
- Translate table names: [schema].[table] -> schema_table
- Translate placeholders: ? -> %s
- Translate MERGE statements to INSERT ... ON DUPLICATE KEY UPDATE

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

config/schema.py

@@ -44,17 +44,34 @@ class DatabaseConfig:
     driver: str = "ODBC Driver 18 for SQL Server"
     trust_server_certificate: str = "yes"
 
+    # MySQL 支持字段
+    db_type: str = "sqlserver"  # "sqlserver" 或 "mysql"
+    host: Optional[str] = None   # MySQL 主机地址
+    port: Optional[int] = None   # MySQL 端口
+
     def validate(self) -> list[str]:
         """验证配置，返回错误列表"""
         errors = []
-        if not self.server:
-            errors.append("数据库服务器地址不能为空")
+
+        if self.db_type == "mysql":
+            # MySQL 配置验证
+            if not self.host:
+                errors.append("MySQL 主机地址不能为空")
+            if not self.port:
+                errors.append("MySQL 端口不能为空")
+        else:
+            # SQL Server 配置验证
+            if not self.server:
+                errors.append("数据库服务器地址不能为空")
+
+        # 通用配置验证
         if not self.database:
             errors.append("数据库名称不能为空")
         if not self.username:
             errors.append("数据库用户名不能为空")
         if not self.password:
             errors.append("数据库密码不能为空")
+
         return errors
 
 
@@ -177,6 +194,9 @@ class AppConfig:
                 "password": self.database.password,
                 "driver": self.database.driver,
                 "trust_server_certificate": self.database.trust_server_certificate,
+                "db_type": self.database.db_type,
+                "host": self.database.host,
+                "port": self.database.port,
             },
             "paths": {
                 "data_dir": self.paths.data_dir,