test(schema): add BDD scenarios for uncovered server-qualified name validator branches

Add rejection scenarios for actor names with empty server prefix and
server prefix without namespace slash to cover all error branches in
the updated validate_name method. Add skill rejection scenario for
server-qualified names with multiple slashes for parity with actor tests.

ISSUES CLOSED: #9074

features/actor_schema.feature

@@ -213,6 +213,18 @@ Feature: Actor YAML schema validation
     Then the actor schema validation should fail
     And the validation error should contain "namespaced"
 
+  Scenario: Reject actor with empty server prefix
+    Given an actor YAML string with name ":namespace/name"
+    When I validate the actor schema
+    Then the actor schema validation should fail
+    And the validation error should contain "empty server prefix"
+
+  Scenario: Reject actor with server prefix but no namespace slash
+    Given an actor YAML string with name "dev/server:name"
+    When I validate the actor schema
+    Then the actor schema validation should fail
+    And the validation error should contain "namespace/name after server prefix"
+
   # ────────────────────────────────────────────────────────────
   # Invalid LLM Actor scenarios
   # ────────────────────────────────────────────────────────────

features/skill_schema.feature

@@ -141,6 +141,12 @@ Feature: Skill YAML schema validation
     When I validate the skill schema
     Then the skill schema validation should succeed
 
+  Scenario: Reject skill with server-qualified name but multiple slashes
+    Given a skill YAML string with name "dev:namespace/sub/skill"
+    When I validate the skill schema expecting failure
+    Then the skill schema validation should fail
+    And the skill schema error should mention "namespace/name"
+
   Scenario: Invalid namespaced name with special characters
     Given a skill YAML string with name "local/bad name!!"
     When I validate the skill schema expecting failure