fix(jobengine): register startup migrations for orchestrator schema

Wire AddStartupMigrations so JobEngine converges the orchestrator schema
on fresh database or wiped volumes without manual bootstrap scripts.
Adds StellaOps.Infrastructure.Postgres.Migrations dependency.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/JobEngine/StellaOps.JobEngine/StellaOps.JobEngine.Infrastructure/ServiceCollectionExtensions.cs

@@ -2,6 +2,7 @@
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Npgsql;
+using StellaOps.Infrastructure.Postgres.Migrations;
 using StellaOps.JobEngine.Core.Backfill;
 using StellaOps.JobEngine.Core.DeadLetter;
 using StellaOps.JobEngine.Core.Observability;
@@ -54,6 +55,12 @@ public static class ServiceCollectionExtensions
                 }
             });
 
+        services.AddStartupMigrations<JobEngineServiceOptions>(
+            schemaName: "orchestrator",
+            moduleName: "JobEngine",
+            migrationsAssembly: typeof(JobEngineDataSource).Assembly,
+            connectionStringSelector: options => options.Database.ConnectionString);
+
         // Register data source
         services.AddSingleton<JobEngineDataSource>();