feat(scheduler,packsregistry,registry): postgres backend cutover

Sprint SPRINT_20260415_003_DOCS_scheduler_registry_real_backend_cutover.

- Scheduler WebService: Postgres-backed audit service + resolver job service,
  system schedule bootstrap, durable host tests, jwt app factory
- PacksRegistry: persistence extensions + migration 002 runtime pack repo,
  durable runtime + startup contract tests
- Registry.TokenService: Postgres plan rule store + admin endpoints,
  migration 001 initial schema, durable runtime + persistence tests
- Scheduler.Plugin.Doctor: wiring for doctor job plugin
- Sprint _019 (webhook rate limiter) and _002 (compose storage compat)
  land separately.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/JobEngine/StellaOps.Scheduler.plugins/StellaOps.Scheduler.Plugin.Doctor/DoctorJobPlugin.cs

@@ -195,6 +195,8 @@ public sealed class DoctorJobPlugin : ISchedulerJobPlugin
 
         // Register trend repository
         var connectionString = configuration["Scheduler:Storage:ConnectionString"]
+                               ?? configuration["Scheduler:Storage:Postgres:Scheduler:ConnectionString"]
+                               ?? configuration["Postgres:Scheduler:ConnectionString"]
                                ?? configuration.GetConnectionString("Default")
                                ?? "";
         services.AddSingleton<IDoctorTrendRepository>(sp =>

src/JobEngine/StellaOps.Scheduler.plugins/StellaOps.Scheduler.Plugin.Doctor/Endpoints/DoctorTrendEndpoints.cs

@@ -176,6 +176,6 @@ public static class DoctorTrendEndpoints
             return tenantHeader.ToString();
         }
 
-        return "demo-prod";
+        return "default";
     }
 }