fix(nocgo): validate LatticeNTTMLDSABatch shape before no-backend return

The !cgo path returned ErrNotSupported for any input, but the cgo path
(and TestNoopBehavior) require shape validation first: a wrong-length
poly must be ErrShapeMismatch regardless of build. This was failing the
'Test without CGO (fallback)' CI job (pre-existing, since the op was
implemented). Now CGO=0 and CGO=1 agree.

Co-authored-by: Hanzo Dev <dev@hanzo.ai>
EOF

defaults.go

@@ -97,6 +97,18 @@ func MLDSASignBatch(_ int, _, _ [][]byte, _ int) ([][]byte, error) {
 }
 
 // LatticeNTTMLDSABatch returns ErrNotSupported in non-CGO builds.
-func LatticeNTTMLDSABatch(_ [][]int32, _ bool) error {
+func LatticeNTTMLDSABatch(polys [][]int32, _ bool) error {
+	// Validate the batch shape before the (absent) GPU dispatch decision,
+	// matching the cgo path so callers get the same error regardless of
+	// build: a wrong-length poly is ErrShapeMismatch, empty is
+	// ErrBatchSizeMismatch; otherwise no backend → ErrNotSupported.
+	if len(polys) == 0 {
+		return ErrBatchSizeMismatch
+	}
+	for _, p := range polys {
+		if len(p) != MLDSANTTPolyLen {
+			return ErrShapeMismatch
+		}
+	}
 	return ErrNotSupported
 }