fix(descriptor): rebuild SDP that Firefox accepts; release v5.8.1

Live cross-browser testing found three defects in the SBQ2 SDP template, all
invisible to Chrome and all fatal to Firefox.

The candidate lines omitted raddr/rport on srflx and relay candidates. RFC 8839
section 5.1 makes rel-addr and rel-port mandatory for non-host candidates even
though ICE never reads them; Chrome tolerates the omission and Firefox drops the
candidate. Relay-only connections to Firefox failed 0/8 against 8/8 for the
browser's own SDP. The STUN and TURN profiles hid it because a host pair
connected instead -- the relay candidates were never actually needed there.

The template also advertised ice-options:trickle without ever closing the
candidate set, though a descriptor is a complete one-shot set with no channel to
trickle over, and hard-coded the m= port and c= line to the 9 / 0.0.0.0 null
default candidate, which is the trickle convention for "nothing gathered yet".
Both are now correct: no trickle, an explicit a=end-of-candidates, and the most
publicly reachable candidate as the default.

All three are serializer-side and cost zero descriptor bytes; sizes are
unchanged at 98-149 bytes, QR version 6-8. Verified 48/48 across all 16
combinations of {Chrome, Firefox} squared and four network profiles, with every
relay-only pair now connecting over the relay.

doc/CRYPTOGRAPHY.md

@@ -7,7 +7,7 @@ this document describes.
 
 | | |
 | --- | --- |
-| Release | v5.8.0 |
+| Release | v5.8.1 |
 | Protocol version | 4.1 |
 | Ratchet wire version | 1 |
 
@@ -214,5 +214,5 @@ worse than one that reports nothing.
 
 ## Scope
 
-This describes the browser implementation as it stands in v5.8.0. It is not a
+This describes the browser implementation as it stands in v5.8.1. It is not a
 substitute for independent cryptographic review.