Name exp in the errInvalidFormField comment (closes #72)

parseExpires wraps errInvalidFormField for exp, so its comment names exp
alongside q.

Model: opus-5-5

internal/handlers/auth.go

@@ -18,9 +18,9 @@ import (
 	"sneak.berlin/go/pixa/internal/templates"
 )
 
-// errInvalidFormField reports a generator form field, or the q parameter of
+// errInvalidFormField reports a generator form field, or the q or exp
-// /v1/image/, whose value is non-numeric or out of range. The offending field
+// parameter of /v1/image/, whose value is non-numeric or out of range. The
-// name is wrapped in so the response can name it.
+// offending field name is wrapped in so the response can name it.
 var errInvalidFormField = errors.New("invalid")
 
 // Bounds for the generator's quality and ttl fields; the quality bounds also