Source license headers

Apache-2.0 — Go sources use SPDX at file top (Copyright line optional on older files):

Copyright 2026 Zyvor AI Labs · https://zyvor.dev
SPDX-License-Identifier: Apache-2.0

New files should include both:

Copyright 2026 Zyvor AI Labs · https://zyvor.dev
SPDX-License-Identifier: Apache-2.0

Full license: LICENSE.