Phase 1 WP-11–22: Host infrastructure, Blazor Server UI, and integration tests

Host infrastructure (WP-11–17):
- StartupValidator with 19 validation rules
- /health/ready endpoint with DB + Akka health checks
- Akka.NET bootstrap via AkkaHostedService (HOCON config, cluster, remoting, SBR)
- Serilog with SiteId/NodeHostname/NodeRole enrichment
- DeadLetterMonitorActor with count tracking
- CoordinatedShutdown wiring (no Environment.Exit)
- Windows Service support (UseWindowsService)

Central UI (WP-18–21):
- Blazor Server shell with Bootstrap 5, role-aware NavMenu
- Login/logout flow (LDAP auth → JWT → HTTP-only cookie)
- CookieAuthenticationStateProvider with idle timeout
- LDAP group mapping CRUD page (Admin role)
- Route guards with Authorize attributes per role
- SignalR reconnection overlay for failover

Integration tests (WP-22):
- Startup validation, auth flow, audit transactions, readiness gating
186 tests pass (1 skipped: LDAP integration), zero warnings.

src/ScadaLink.CentralUI/Components/Pages/Login.razor

@@ -0,0 +1,34 @@
+@page "/login"
+
+<div class="container" style="max-width: 400px; margin-top: 10vh;">
+    <div class="card shadow-sm">
+        <div class="card-body p-4">
+            <h4 class="card-title mb-4 text-center">ScadaLink</h4>
+
+            @if (!string.IsNullOrEmpty(ErrorMessage))
+            {
+                <div class="alert alert-danger py-2" role="alert">@ErrorMessage</div>
+            }
+
+            <form method="post" action="/auth/login">
+                <div class="mb-3">
+                    <label for="username" class="form-label">Username</label>
+                    <input type="text" class="form-control" id="username" name="username"
+                           required autocomplete="username" autofocus />
+                </div>
+                <div class="mb-3">
+                    <label for="password" class="form-label">Password</label>
+                    <input type="password" class="form-control" id="password" name="password"
+                           required autocomplete="current-password" />
+                </div>
+                <button type="submit" class="btn btn-primary w-100">Sign In</button>
+            </form>
+        </div>
+    </div>
+    <p class="text-center text-muted mt-3 small">Authenticate with your organization's LDAP credentials.</p>
+</div>
+
+@code {
+    [SupplyParameterFromQuery(Name = "error")]
+    public string? ErrorMessage { get; set; }
+}