Add IDesignTimeDbContextFactory for pipeline EF bundle

Shogi/BackEnd/Identity/ApplicationDbContextFactory.cs

@@ -0,0 +1,18 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Design;
+
+namespace Shogi.BackEnd.Identity;
+
+public class ApplicationDbContextFactory : IDesignTimeDbContextFactory<ApplicationDbContext>
+{
+    public ApplicationDbContext CreateDbContext(string[] args)
+    {
+        var optionsBuilder = new DbContextOptionsBuilder<ApplicationDbContext>();
+
+        // This connection string is strictly for design-time tools (like creating migrations).
+        // It is NOT used when running the app or when applying the migration bundle.
+        optionsBuilder.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=ShogiDb;Trusted_Connection=True;MultipleActiveResultSets=true");
+
+        return new ApplicationDbContext(optionsBuilder.Options);
+    }
+}