Sonic 2 v0.8.2 - 4-player online rooms

Online rooms now start with 3 or 4 players. Since the lobby server retired its relay, anything above 2 players was refused at Start, so rooms effectively capped at 2.

What changed

• 2-player rooms connect peer-to-peer (ICE). No port forwarding needed.
• 3–4 player rooms: the host carries the match on their own UDP port (7777 by default). The game opens it automatically via UPnP / NAT-PMP when the router allows; otherwise the host must forward UDP 7777. If a guest can't reach the host, Start is refused with a reason instead of launching a smaller match.
• Rooms default to 4 seats.
• Updated netplay libraries (recomp-net, recomp-ui) to match the current lobby server.

Playing together

1. Everyone uses this v0.8.2 ZIP (lobbies only match the same version) and supplies their own Sonic 2 Rev A ROM.
2. Host creates an online lobby (Max Players 4), everyone joins, host presses Play. If Start is refused right after the last player joins, wait a few seconds and press Play again.
3. LAN / Direct IP rooms remain 2 players.

Validated on loopback against the current lobby server: 2, 3 and 4 player matches ran 1800 frames with 0 desyncs; LAN unchanged; 28/28 tests. Real internet / NAT play has not been tested yet — please report how it goes.