fix: 修复主键类型非Integer时的模型生成与导入问题

1. 前端将MySQL主键默认类型从bigint改为int，同步后端代码适配
2. 增加SQLAlchemy主键类型自动导入逻辑，当主键类型不是Integer时自动添加对应导入
3. 重构模型模板，当主键类型与基类不一致时显式覆盖id字段定义

frontend/web/src/views/module_generator/gencode/utils/createTableVisualPresets.ts

@@ -94,7 +94,7 @@ function pkMysql(): ColDef[] {
   return [
     {
       name: "id",
-      type: "bigint",
+      type: "int",
       nullable: false,
       isPk: true,
       comment: "主键ID",
@@ -129,7 +129,7 @@ function buildSubColumns(dialect: SqlDialect, mainTableName: string, fkColumn: s
   const subPk = isMysql ? pkMysql() : pkPostgres();
   const fkColDef: ColDef = {
     name: fkColumn,
-    type: "bigint",
+    type: isMysql ? "int" : "integer",
     nullable: false,
     isPk: false,
     comment: `关联 ${mainTableName}.${"id"}`,