Mbed TLS vendor provenance

Version: 3.6.7 (3.6 LTS maintenance release). Upstream: https://github.com/Mbed-TLS/mbedtls/releases/tag/mbedtls-3.6.7 Archive: https://github.com/Mbed-TLS/mbedtls/releases/download/mbedtls-3.6.7/mbedtls-3.6.7.tar.bz2 SHA256: a7e8bcbec0e6f761b4af24f25677626b35f762f68eef79c08677a363212d11f6

Verified against the official release checksum and release asset digest. The archive is mirrored under mbedtls/. The only Sigil-specific file there is sigil_mbedtls_config.h; upstream library and header sources are unmodified. TLS 1.3 uses PSA with capabilities derived from the enabled legacy algorithms. The configuration retains TLS 1.2 and enables certificate-based ephemeral TLS 1.3 handshakes, without session tickets, PSK or early data.