core: type operation timestamps

crates/crank-registry/src/model.rs

@@ -211,9 +211,9 @@ pub struct OperationSummary {
     pub status: OperationStatus,
     pub current_draft_version: u32,
     pub latest_published_version: Option<u32>,
-    pub created_at: String,
-    pub updated_at: String,
-    pub published_at: Option<String>,
+    pub created_at: OffsetDateTime,
+    pub updated_at: OffsetDateTime,
+    pub published_at: Option<OffsetDateTime>,
 }
 
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
@@ -239,7 +239,7 @@ pub struct OperationVersionRecord {
     pub version: u32,
     pub status: OperationStatus,
     pub change_note: Option<String>,
-    pub created_at: String,
+    pub created_at: OffsetDateTime,
     pub created_by: Option<String>,
     pub snapshot: RegistryOperation,
 }
@@ -370,7 +370,7 @@ pub struct PublishRequest<'a> {
     pub workspace_id: &'a WorkspaceId,
     pub operation_id: &'a OperationId,
     pub version: u32,
-    pub published_at: &'a str,
+    pub published_at: &'a OffsetDateTime,
     pub published_by: Option<&'a str>,
 }