Instead of echoing the first cipher suite from ClientHello (which is
often a GREASE value like 0x5a5a), iterate the list and pick the first
real cipher suite. This is what real TLS servers do per RFC 8701.
Production data shows two client profiles:
- 87% send GREASE first, then 0x1301 (TLS_AES_128_GCM_SHA256)
- 13% send 0xc02b first (TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256)
The fix correctly selects 0x1301 or 0xc02b respectively, matching
real server behavior. Fallback to 0x1301 if all suites are GREASE.
Add snapshot test with GREASE as first cipher suite.
