refactor: implement standard Razor Pages login at /Account/Login

Remove all workarounds and implement proper ASP.NET Core structure:

❌ REMOVED (편법):
  - Pages/Login.cshtml (root path workaround)
  - wwwroot/login.html (static file bypass)
  - MapGet("/login") middleware hack

✅ IMPLEMENTED (정석):
  - Pages/Account/Login.cshtml (standard Razor Pages)
  - Pages/Account/Login.cshtml.cs (code-behind)
  - Standard /Account/Login URL pattern
  - MapRazorPages() only (no custom routing)

Benefits:
  • Follows ASP.NET Core conventions
  • No Blazor routing conflicts
  • Clean separation of concerns
  • Maintainable and extensible
  • Standard URL pattern (/Account/Login)
  • Professional structure for team development

Testing:
  ✅ Razor Pages rendering: PASS
  ✅ E2E login test: PASS (10.7s)
  ✅ API endpoint: 200 OK
  ✅ Home redirect: SUCCESS
  ✅ Dashboard content: VERIFIED

The proper, standards-compliant solution is now ready.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/dotnet/QuantEngine.Web/Program.cs

@@ -415,12 +415,9 @@ app.MapPost("/api/history/{domain}", async (string domain, JsonElement payload,
     });
 });
 
-// Razor Pages (로그인 등)
+// Razor Pages (Account/Login)
 app.MapRazorPages();
 
-// 정적 로그인 페이지 (wwwroot/login.html)
-app.MapGet("/login", () => Results.File("wwwroot/login.html", "text/html"));
-
 app.MapRazorComponents<App>()
     .AddInteractiveServerRenderMode()
     .AddInteractiveWebAssemblyRenderMode()