feat: Migrate admin UI from Blazor WASM/MudBlazor to Razor Pages/Cookie Auth/Tabler

- Remove QuantEngine.Web.Client from .sln (keep on disk for reference)
- Replace Blazor Interactive WebAssembly with server-rendered Razor Pages
- Implement Cookie Authentication (HttpOnly, SameSite=Lax, 12h expiry)
- Add AuthService with BCrypt password hashing + auto-migration from SHA-256
- Implement IpLockoutService (3 strikes → 15-min ban)
- Create Admin folder structure with Layout + shared partials
- Implement Dashboard, Collection, Users index pages (base structure)
- Remove hardcoded backdoors (master_recovery, dev auth bypass)
- Remove hardcoded localhost:5265 URLs
- Add Tabler UI base styling (Bootstrap 5 CDN + custom admin.css)
- Update CLAUDE.md with new UI standards and auth policies
- Build: 0 errors, 0 warnings (ready for dev testing)

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

src/dotnet/QuantEngine.Web/Models/PaginationModel.cs

@@ -0,0 +1,3 @@
+namespace QuantEngine.Web.Models;
+
+public sealed record PaginationModel(int Page, int TotalPages, Func<int, string> BuildPageUrl);