docs(aura-engine): SweepError summary names RandomSpace::new too

The SweepError type-level rustdoc still read "A structural fault constructing a
`GridSpace`" though the enum now also gates `RandomSpace::new` (the three
random-only variants are each documented individually, but the type summary was
stale). Broaden it to name both spaces and group the grid vs. random faults.
Doc-only, behaviour-preserving — the same low-grade doc-debt class the 0049
audit fixed inline for the module doc. Surfaced by the cycle-0049 fieldtest.

refs #52

crates/aura-engine/src/sweep.rs

@@ -118,7 +118,9 @@ impl Space for GridSpace {
     }
 }
 
-/// A structural fault constructing a `GridSpace` — the typed gate before any run.
+/// A structural fault constructing a `GridSpace` or a `RandomSpace` — the shared
+/// typed gate before any run (grid faults: `Arity` / `KindMismatch` / `EmptyAxis`;
+/// random faults: `NonNumericRange` / `RangeKindMismatch` / `EmptyRange`).
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum SweepError {
     /// The number of axes does not equal the param-space slot count.