Refine remaining components: Deployment Manager, Central UI, Site Event Logging, S&F

Deployment Manager: add deployment concurrency rules (block same-instance, allow
parallel different-instance), per-site artifact deployment status, current-only
status persistence.

Central UI: specify Blazor Server framework, real-time push updates via SignalR
for debug view, health dashboard, and deployment status.

Site Event Logging: daily retention purge, paginated queries with 500-event default,
keyword search on message/source fields.

Store-and-Forward: clarify async best-effort replication to standby with acceptable
trade-offs on failover.

Component-CentralUI.md

@@ -8,6 +8,22 @@ The Central UI is a web-based management interface hosted on the central cluster
 
 Central cluster only. Sites have no user interface.
 
+## Technology
+
+- **Framework**: Blazor Server (ASP.NET Core). UI logic executes on the server, updates pushed to the browser via SignalR.
+- Keeps the entire stack in C#/.NET, consistent with the rest of the system (Akka.NET, EF Core).
+- SignalR provides built-in support for real-time UI updates.
+
+## Real-Time Updates
+
+All real-time features use **server push via SignalR** (built into Blazor Server):
+
+- **Debug view**: Attribute value and alarm state changes streamed live from sites.
+- **Health dashboard**: Site status, connection health, error rates, and buffer depths update automatically when new health reports arrive.
+- **Deployment status**: Pending/in-progress/success/failed transitions push to the UI immediately.
+
+No manual refresh or polling is required for any of these features.
+
 ## Responsibilities
 
 - Provide authenticated access to all management workflows.