feat(admin): restore Blazor WebAssembly architecture for admin pages with hybrid Server routing

TaxBaik.Web.Client/Services/ITokenStore.cs

@@ -0,0 +1,39 @@
+namespace TaxBaik.Web.Services;
+
+/// <summary>
+/// Scoped in-memory token store for Blazor Server.
+/// SOLID: Single Responsibility - Token lifecycle management
+/// Avoids JS interop from DelegatingHandler (which runs on non-circuit thread)
+/// </summary>
+public interface ITokenStore
+{
+    string? AccessToken { get; set; }
+    string? RefreshToken { get; set; }
+    long? TokenExpiryTicks { get; set; }
+
+    bool IsAccessTokenExpired();
+    void Clear();
+}
+
+public class TokenStore : ITokenStore
+{
+    public string? AccessToken { get; set; }
+    public string? RefreshToken { get; set; }
+    public long? TokenExpiryTicks { get; set; }
+
+    public bool IsAccessTokenExpired()
+    {
+        if (TokenExpiryTicks == null)
+            return true;
+
+        var expiryTime = new DateTime(TokenExpiryTicks.Value, DateTimeKind.Utc);
+        return expiryTime <= DateTime.UtcNow;
+    }
+
+    public void Clear()
+    {
+        AccessToken = null;
+        RefreshToken = null;
+        TokenExpiryTicks = null;
+    }
+}