plan: 0103 fix — derive(Debug) on ScaffoldSpec

The Task-1 unit tests call unwrap_err() on Result<ScaffoldSpec, String>,
which requires ScaffoldSpec: Debug; the prescribed struct lacked the
derive, so the plan's own bytes could not compile. The implement loop
correctly blocked on the necessary deviation (spec-compliance holds
verbatim plan code); this aligns the plan with the only compiling form.

refs #180

docs/plans/0103-aura-new-scaffolder.md

@@ -53,6 +53,7 @@ Everything else is untouched — the verb is additive.
 
 use std::path::{Path, PathBuf};
 
+#[derive(Debug)]
 pub struct ScaffoldSpec {
     pub name: String,
     pub namespace: String,