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-SiteEventLogging.md

@@ -41,7 +41,7 @@ Each event entry contains:
 
 - Events are stored in **local SQLite** on each site node.
 - Each node maintains its own event log (the active node generates events; the standby node generates minimal events related to replication).
-- **Retention**: 30 days. A background job automatically purges events older than 30 days.
+- **Retention**: 30 days. A **daily background job** runs on the active node and deletes all events older than 30 days. Hard delete — no archival.
 
 ## Central Access
 
@@ -51,7 +51,9 @@ Each event entry contains:
   - Time range
   - Instance ID
   - Severity
-- The site processes the query locally and returns matching results to central.
+  - **Keyword search**: Free-text search on message and source fields (SQLite LIKE query). Useful for finding events by script name, alarm name, or error message across all instances.
+- Results are **paginated** with a configurable page size (default: 500 events). Each response includes a continuation token for fetching additional pages. This prevents broad queries from overwhelming the communication channel.
+- The site processes the query locally against SQLite and returns matching results to central.
 
 ## Dependencies