Remove invalid validation checks

- Stop checking metadata on epic interactions (steps don't require it)
- Allow 'external' option on Context in addition to Domain

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

Author: reid-spencer

passes/shared/src/main/scala/com/ossuminc/riddl/passes/validate/DefinitionValidation.scala

@@ -97,7 +97,7 @@ object RecognizedOptions:
     // Icon and display options
     "faicon" -> OptionSpec(Seq.empty, 1, 1),
     // Domain/Context structural options
-    "external" -> OptionSpec(Seq("Domain"), 0, 0),
+    "external" -> OptionSpec(Seq("Domain", "Context"), 0, 0),
     "namespace" -> OptionSpec(Seq("Domain", "Context"), 1, 1),
     "package" -> OptionSpec(Seq("Domain", "Context"), 1, 1)
   )

passes/shared/src/main/scala/com/ossuminc/riddl/passes/validate/ValidationPass.scala

@@ -161,8 +161,8 @@ case class ValidationPass(
         validateContext(c, parentsAsSeq)
       case d: Domain =>
         validateDomain(d, parentsAsSeq)
-      case s: Epic =>
-        validateEpic(s, parentsAsSeq)
+      case e: Epic =>
+        validateEpic(e, parentsAsSeq)
       case uc: UseCase =>
         validateUseCase(uc, parentsAsSeq)
       case grp: Group =>
@@ -1236,7 +1236,7 @@ case class ValidationPass(
   // FIXME: This should be used
   private def validateInteraction(interaction: Interaction, parents: Parents): Unit = {
     val useCase = parents.head
-    checkMetadata(useCase.identify, interaction, interaction.loc)
+    // checkMetadata(useCase.identify, interaction, interaction.loc)
     interaction match {
       case SelfInteraction(_, from, _, _) =>
         checkRef[Definition](from, parents)