fix(release): create download directories, refuse duplicate asset names and empty notes (follow gh)

Signed-off-by: bircni <bircni@icloud.com>

internal/app/validation_test.go

@@ -147,6 +147,7 @@ func TestUsageErrorsPrecedeRequests(t *testing.T) {
 		{[]string{"release", "create", "v1", "--tag", "v2"}, "supply a tag argument or --tag, not both"},
 		{[]string{"release", "create", "--body-file", "-"}, "--notes-file - requires a tag"},
 		{[]string{"release", "edit", "v1"}, "supply release fields to edit"},
+		{[]string{"release", "edit", "v1", "--notes", ""}, "release notes cannot be cleared"},
 		{[]string{"release", "edit", "v1", "v2", "--tag", "v3"}, "--tag requires one release and a nonempty new tag"},
 		{[]string{"release", "edit", "v1", "--draft", "false"}, "--draft takes no value; use --draft or --draft=false"},
 		{[]string{"release", "edit", "v1", "-d", "false", "-p", "False"}, "--draft takes no value; use --draft or --draft=false"},