core: type user and auth session timestamps

crates/crank-registry/src/postgres/workspace.rs

@@ -1,4 +1,5 @@
 use super::*;
+use time::OffsetDateTime;
 
 impl PostgresRegistry {
     pub async fn list_workspaces(&self) -> Result<Vec<WorkspaceRecord>, RegistryError> {
@@ -88,7 +89,7 @@ impl PostgresRegistry {
                 u.email,
                 u.display_name,
                 u.status,
-                to_char(u.created_at at time zone 'UTC', 'YYYY-MM-DD\"T\"HH24:MI:SS\"Z\"') as \"user_created_at!\"
+                u.created_at as \"user_created_at!: OffsetDateTime\"
              from memberships m
              join users u on u.id = m.user_id
              where m.workspace_id = $1