docs: enumerate RELAY handshake and emergency subtypes in frame catalog

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

mlnl_chunk_spec.md

@@ -136,7 +136,10 @@ assertion_failed  t_start = watch start, t_end = watch deadline
 `PRESENCE/GEOPOLL_RESP`, `PRESENCE/SEED`, `PRESENCE/SEED_ACK`, `BULK/RTS`,
 `BULK/ACK`, `BULK/DNAK`, `BULK/SBSERIES`, `BULK/SBRTS`, `BULK/RETX_RTS`,
 `BULK/SB_RETX_RTS`, `BULK/INET_REQ`, `BULK` (one OFDM data frame),
-`SHORTBURST` (one strung-announce data frame), `RELAY`, `APRS`. New names
+`SHORTBURST` (one strung-announce data frame), `RELAY` (plus the relay
+handshake subtypes `RELAY/REQUEST`, `RELAY/OFFER`, `RELAY/SELECT`,
+`RELAY/FOR`, `RELAY/RESULT`, and the strung emergency rebroadcast
+`RELAY/EMERG` / Authoritative ACK `RELAY/EMERG_ACK`), `APRS`. New names
 appear as the protocol grows — treat `frame` as a free-form short string.
 
 **REMOVED — `tx_burst`** (energy-detected): the channel's old *guess* at "a