feat: 新增微信 OAuth 公开配置接口

从其他配置 wechat_mp 返回 AppId 与 OAuthRedirectBase，供 H5 网页授权使用。

Co-authored-by: Cursor <cursoragent@cursor.com>

src/SimpleAdmin.Api.IntegrationTests/WeChatRouteIntegrationTests.cs

@@ -32,6 +32,7 @@ public class WeChatRouteIntegrationTests
         host.RoutePatterns.Should().Contain("apiwechat/verification");
         host.RoutePatterns.Should().Contain("wechat/mp/{appId}");
         host.RoutePatterns.Should().Contain("wechat/mp/login-qrcode");
+        host.RoutePatterns.Should().Contain("wechat/mp/oauth-config");
         host.RoutePatterns.Should().Contain("wechat/mp/follow-qrcode");
         host.RoutePatterns.Should().Contain("wechat/oauth/user-info");
         host.RoutePatterns.Should().Contain("wechat/customer/register");

src/SimpleAdmin.Api/Auth/AuthService.WeChatMp.cs

@@ -159,6 +159,31 @@ public partial class AuthService
             cancellationToken);
     }
 
+    /// <summary>
+    /// H5 网页授权公开配置：AppId + OAuth 回调根（来自其他配置 wechat_mp）。
+    /// </summary>
+    [AllowAnonymous]
+    [HttpGet("/wechat/mp/oauth-config")]
+    [ApiExplorerSettings(GroupName = "WeChat")]
+    public async Task<WxOAuthConfigOutput> GetWeChatOAuthConfigAsync(
+        CancellationToken cancellationToken = default)
+    {
+        var options = await WeChatMpConfigProvider.GetAsync(cancellationToken);
+        if (string.IsNullOrWhiteSpace(options.AppId))
+        {
+            throw new BusinessException(
+                "未配置微信公众号 AppId。请在「其他配置」维护 wechat_mp，AppKey 填公众号 AppId。");
+        }
+
+        return new WxOAuthConfigOutput
+        {
+            AppId = options.AppId.Trim(),
+            OAuthRedirectBase = string.IsNullOrWhiteSpace(options.OAuthRedirectBase)
+                ? null
+                : options.OAuthRedirectBase.Trim().TrimEnd('/')
+        };
+    }
+
     /// <summary>
     /// 获取 PC 扫码登录二维码。
     /// </summary>

src/SimpleAdmin.Api/WeChat/Dtos/WeChatDtos.cs

@@ -12,6 +12,19 @@ public class WxLoginQrcodeOutput
     public int ExpiresIn { get; set; } = 600;
 }
 
+/// <summary>H5 网页授权所需公开配置（不含 Secret/Token）。</summary>
+public class WxOAuthConfigOutput
+{
+    /// <summary>公众号 AppId（来自其他配置 wechat_mp.AppKey）。</summary>
+    public string AppId { get; set; } = string.Empty;
+
+    /// <summary>
+    /// OAuth 回调根地址（来自 wechat_mp.BaseUrl），如 https://ideship.com。
+    /// 为空时前端回退到当前页面 origin。
+    /// </summary>
+    public string? OAuthRedirectBase { get; set; }
+}
+
 /// <summary>引导关注公众号：优先返回可直接跳转的公众号链接。</summary>
 public class WxFollowQrcodeOutput
 {