feat(web): migrate account and user management to React

Add React account and user administration flows, including TOTP and SSO handling. Route /next SSO callbacks to React while preserving the existing Vue and native app behavior, and cover the routing policy with API tests.

tests/Jiaowu.Api.Tests/SsoControllerTests.cs

@@ -119,6 +119,23 @@ public sealed class SsoControllerTests
         Assert.Equal(expected, SsoController.NormalizeReturnUrl(value));
     }
 
+    [Theory]
+    [InlineData("/dashboard", "sso/callback", false, "/sso/callback")]
+    [InlineData("/next/dashboard", "sso/callback", false, "/next/sso/callback")]
+    [InlineData("/next/account", "account", false, "/next/account")]
+    [InlineData("/next/dashboard", "sso/callback", true, "/sso/callback")]
+    [InlineData("https://evil.example/path", "login", false, "/login")]
+    public void FrontendPagePath_SelectsReactOnlyForNextWebRoutes(
+        string? returnUrl,
+        string page,
+        bool nativeApp,
+        string expected)
+    {
+        Assert.Equal(
+            expected,
+            SsoController.FrontendPagePath(returnUrl, page, nativeApp));
+    }
+
     private sealed class BindingFixture : IAsyncDisposable
     {
         private readonly SqliteConnection _connection;