feat(concelier): accept environment name or GUID in readiness endpoint

The /environments/{id}/readiness endpoint now resolves environment names
(e.g. "dev", "prod-us-east") via IEnvironmentService, returning an empty
list for unregistered environments instead of a 404.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/Concelier/StellaOps.Concelier.WebService/Extensions/TopologySetupEndpointExtensions.cs

@@ -5,6 +5,7 @@ using StellaOps.ReleaseOrchestrator.Environment.InfrastructureBinding;
 using StellaOps.ReleaseOrchestrator.Environment.Readiness;
 using StellaOps.ReleaseOrchestrator.Environment.Region;
 using StellaOps.ReleaseOrchestrator.Environment.Rename;
+using StellaOps.ReleaseOrchestrator.Environment.Services;
 using EnvModels = StellaOps.ReleaseOrchestrator.Environment.Models;
 
 namespace StellaOps.Concelier.WebService.Extensions;
@@ -365,12 +366,37 @@ internal static class TopologySetupEndpointExtensions
         var envs = app.MapGroup("/api/v1/environments")
             .WithTags("Topology Readiness");
 
-        envs.MapGet("/{id:guid}/readiness", async (
-            Guid id,
+        // Accept GUID or environment name (e.g. "dev", "stage", "prod-us-east").
+        // Returns an empty list when the environment has no targets registered yet.
+        envs.MapGet("/{id}/readiness", async (
+            string id,
             [FromServices] ITopologyReadinessService readinessService,
+            [FromServices] IEnvironmentService environmentService,
             CancellationToken ct) =>
         {
-            var reports = await readinessService.ListByEnvironmentAsync(id, ct);
+            Guid? environmentId = null;
+            if (Guid.TryParse(id, out var parsed))
+            {
+                environmentId = parsed;
+            }
+            else
+            {
+                var env = await environmentService.GetByNameAsync(id, ct);
+                if (env is not null)
+                    environmentId = env.Id;
+            }
+
+            // Environment not yet registered in orchestrator → empty readiness (not an error)
+            if (environmentId is null)
+            {
+                return HttpResults.Ok(new ReadinessListResponse
+                {
+                    Items = [],
+                    TotalCount = 0
+                });
+            }
+
+            var reports = await readinessService.ListByEnvironmentAsync(environmentId.Value, ct);
             return HttpResults.Ok(new ReadinessListResponse
             {
                 Items = reports.Select(MapReport).ToList(),