Fix: Outbox relay has no dead-letter or max retry limit + DataLake writer partial commit inconsistency + ThresholdCacheLoader crashes startup on Redis failure

VigilCareClinicalAPI/Domains/Entities/OutboxEvent.cs

@@ -6,4 +6,7 @@ public class OutboxEvent
     public string? PartitionKey { get; set; }   // encounter_id for all clinical events
     public DateTimeOffset CreatedAt { get; set; }
     public DateTimeOffset? ProcessedAt { get; set; }
+    public int RetryCount { get; set; }
+    public string? LastError { get; set; }
+    public DateTimeOffset? FailedAt { get; set; }
 }