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/Layout/MainLayout.razor

@@ -0,0 +1,8 @@
+@inherits LayoutComponentBase
+
+<div class="d-flex">
+    <NavMenu />
+    <main class="flex-grow-1 p-3" style="min-height: 100vh; background-color: #f8f9fa;">
+        @Body
+    </main>
+</div>