Fix registry lookup E2E: add dummy server to pass validation

The upstream registry file validator requires at least one server or
group. Our test JSON had only skills with an empty servers array, which
was rejected with 502. Add a minimal dummy server entry to satisfy the
validation while keeping the focus on skill resolution.

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

Author: JAORMX

test/e2e/api_skills_test.go

@@ -226,7 +226,21 @@ func createUpstreamRegistryWithSkill(skillName, ociReference string) string {
 		"version": "1.0.0",
 		"meta":    map[string]string{"last_updated": "2025-01-01T00:00:00Z"},
 		"data": map[string]interface{}{
-			"servers": []interface{}{},
+			// A dummy server is required because the config validator rejects
+			// upstream registry files that contain no servers or groups.
+			"servers": []map[string]interface{}{
+				{
+					"name":        "dummy-server",
+					"description": "Placeholder to satisfy registry validation",
+					"repository": map[string]string{
+						"url":  "https://github.com/example/dummy",
+						"type": "git",
+					},
+					"version_detail": map[string]string{
+						"version": "0.0.1",
+					},
+				},
+			},
 			"skills": []map[string]interface{}{
 				{
 					"namespace":   "e2e-test",
@@ -974,9 +988,7 @@ var _ = Describe("Skills API", Label("api", "api-clients", "skills", "e2e"), fun
 	})
 
 	Describe("Registry lookup install", func() {
-		// TODO(#4200): The upstream registry JSON schema validation rejects
-		// the test fixture. Debug the exact required fields and re-enable.
-		PIt("should resolve a plain name from the registry and install from OCI", func() {
+		It("should resolve a plain name from the registry and install from OCI", func() {
 			skillName := "registry-lookup-skill"
 
 			By("Starting an in-process OCI registry")