fix(agents/postdeploy): make postdeploy non-fatal after successful deploy

The postdeploy event handler runs AFTER the agent is already deployed
and active. Failures in this step (AZURE_TENANT_ID missing, agent
version lookup 404, RBAC assignment errors) should not cause azd up
to report EXIT 1 when the deploy actually succeeded.

Wrap the postdeploy handler to catch all errors and emit a warning
to stderr instead of returning the error to azd (which treats it as
a deployment failure).

Discovered via iterative quickstart assessment:
- Iter1: AZURE_TENANT_ID not set → EXIT 1
- Iter3: duplicate service → version lookup 404 → EXIT 1
Both cases had working agents despite the error.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Vivek Bhadauria

cli/azd/extensions/azure.ai.agents/internal/cmd/listen.go

@@ -49,7 +49,14 @@ func configureExtensionHost(host *azdext.ExtensionHost) {
 			return predeployHandler(ctx, azdClient, args)
 		}).
 		WithProjectEventHandler("postdeploy", func(ctx context.Context, args *azdext.ProjectEventArgs) error {
-			return postdeployHandler(ctx, azdClient, args)
+			if err := postdeployHandler(ctx, azdClient, args); err != nil {
+				// Postdeploy runs AFTER the agent is successfully deployed.
+				// Failures here (RBAC assignment, version lookup) are non-fatal
+				// — the agent is already live. Warn and continue.
+				_, _ = fmt.Fprintf(os.Stderr, "\n⚠ Post-deploy step failed (non-fatal): %v\n"+
+					"  Your agent deployed successfully. This step handles optional RBAC setup.\n\n", err)
+			}
+			return nil
 		}).
 		WithProjectEventHandler("postdown", func(ctx context.Context, args *azdext.ProjectEventArgs) error {
 			return postdownHandler(ctx, azdClient, args)