feat: Implement MongoDB orchestrator storage with registry, commands, and heartbeats

- Added NullAdvisoryObservationEventTransport for handling advisory observation events.
- Created IOrchestratorRegistryStore interface for orchestrator registry operations.
- Implemented MongoOrchestratorRegistryStore for MongoDB interactions with orchestrator data.
- Defined OrchestratorCommandDocument and OrchestratorCommandRecord for command handling.
- Added OrchestratorHeartbeatDocument and OrchestratorHeartbeatRecord for heartbeat tracking.
- Created OrchestratorRegistryDocument and OrchestratorRegistryRecord for registry management.
- Developed tests for orchestrator collections migration and MongoOrchestratorRegistryStore functionality.
- Introduced AirgapImportRequest and AirgapImportValidator for air-gapped VEX bundle imports.
- Added incident mode rules sample JSON for notifier configuration.

src/Notifier/StellaOps.Notifier/StellaOps.Notifier.WebService/Program.cs

@@ -126,10 +126,6 @@ app.MapGet("/.well-known/openapi", (HttpContext context, OpenApiDocumentCache ca
     return Results.Content(cache.Document, "application/yaml");
 });
 
-app.Run();
-
-public partial class Program;
-
 static object Error(string code, string message, HttpContext context) => new
 {
     error = new
@@ -139,3 +135,7 @@ static object Error(string code, string message, HttpContext context) => new
         traceId = context.TraceIdentifier
     }
 };
+
+app.Run();
+
+public partial class Program;