feat(auth): 添加微信小程序登录支持

- 新增 wechat_users 表迁移和 SeaORM Entity
- 实现微信登录 Service（code→openid→绑定状态查询）
- 实现手机号绑定 Service（创建/关联 user + 签发 JWT）
- 添加公开路由 POST /auth/wechat/login 和 /auth/wechat/bind-phone
- 新增 WechatConfig 到 AppConfig（appid/secret 通过环境变量配置）
- 添加 reqwest 依赖用于调用微信 jscode2session API

crates/erp-auth/src/entity/mod.rs

@@ -9,3 +9,4 @@ pub mod user_credential;
 pub mod user_department;
 pub mod user_role;
 pub mod user_token;
+pub mod wechat_user;

crates/erp-auth/src/entity/wechat_user.rs

@@ -0,0 +1,38 @@
+use sea_orm::entity::prelude::*;
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Debug, PartialEq, DeriveEntityModel, Serialize, Deserialize)]
+#[sea_orm(table_name = "wechat_users")]
+pub struct Model {
+    #[sea_orm(primary_key, auto_increment = false)]
+    pub id: Uuid,
+    pub tenant_id: Uuid,
+    pub openid: String,
+    #[sea_orm(column_name = "union_id")]
+    pub union_id: Option<String>,
+    pub user_id: Uuid,
+    pub phone: Option<String>,
+    pub created_at: DateTimeUtc,
+    pub updated_at: DateTimeUtc,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub deleted_at: Option<DateTimeUtc>,
+}
+
+#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
+pub enum Relation {
+    #[sea_orm(
+        belongs_to = "super::user::Entity",
+        from = "Column::UserId",
+        to = "super::user::Column::Id",
+        on_delete = "Cascade"
+    )]
+    User,
+}
+
+impl Related<super::user::Entity> for Entity {
+    fn to() -> RelationDef {
+        Relation::User.def()
+    }
+}
+
+impl ActiveModelBehavior for ActiveModel {}