Allow signature requests only on current published version

Requesting a signature only validated that the version was PUBLISHED, so a
signature could be requested on a superseded (older) published version. Reject
versions that are not the document's current published major/minor, and hide
the request button in the console for non-current versions.

Signed-off-by: Sacha Al Himdani <sacha@probo.com>

pkg/server/api/mcp/v1/schema.resolvers.go

@@ -2456,6 +2456,10 @@ func (r *Resolver) RequestDocumentVersionSignatureTool(ctx context.Context, req
 		},
 	)
 	if err != nil {
+		if _, ok := errors.AsType[*probo.ErrDocumentVersionNotCurrent](err); ok {
+			return nil, types.RequestDocumentVersionSignatureOutput{}, fmt.Errorf("cannot request signature: %w", err)
+		}
+
 		panic(fmt.Errorf("cannot request signature: %w", err))
 	}