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/Shared/NotAuthorizedView.razor

@@ -0,0 +1,7 @@
+<div class="container mt-5">
+    <div class="alert alert-warning" role="alert">
+        <h5 class="alert-heading">Not Authorized</h5>
+        <p class="mb-0">You do not have permission to access this page. Contact your administrator if you believe this is an error.</p>
+    </div>
+    <a href="/" class="btn btn-outline-primary btn-sm">Return to Dashboard</a>
+</div>