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/wwwroot/css/admin.css

@@ -0,0 +1,88 @@
+/* QuantEngine Admin UI Styles */
+
+:root {
+    --primary-color: #3f51b5;
+}
+
+body {
+    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
+}
+
+.page {
+    display: flex;
+    min-height: 100vh;
+}
+
+.navbar-brand-image {
+    width: auto;
+    height: 36px;
+}
+
+.page-wrapper {
+    flex: 1;
+    display: flex;
+    flex-direction: column;
+}
+
+.container-xl {
+    flex: 1;
+    padding: 2rem 1rem;
+}
+
+.btn-link {
+    color: var(--primary-color);
+    text-decoration: none;
+}
+
+.btn-link:hover {
+    text-decoration: underline;
+}
+
+.empty {
+    text-align: center;
+    padding: 3rem 1rem;
+}
+
+.empty-header {
+    font-size: 3rem;
+    margin-bottom: 1rem;
+}
+
+.empty-title {
+    font-size: 1.5rem;
+    font-weight: 600;
+}
+
+.empty-subtitle {
+    color: #6c757d;
+    margin-bottom: 2rem;
+}
+
+.page-header {
+    margin-bottom: 2rem;
+}
+
+.page-header .page-title {
+    font-size: 2rem;
+    font-weight: 600;
+}
+
+.card {
+    border: none;
+    border-radius: 0.375rem;
+    box-shadow: 0 0.125rem 0.25rem rgba(0, 0, 0, 0.075);
+}
+
+.badge {
+    padding: 0.375rem 0.75rem;
+    font-weight: 500;
+}
+
+.table-vcenter tbody tr td {
+    vertical-align: middle;
+}
+
+.btn-sm {
+    padding: 0.375rem 0.75rem;
+    font-size: 0.875rem;
+}