Replace the boolean-flag-based async join system with a clean state machine
(eJoinState enum) and move connection progress handling from UIScene_JoinMenu
into UIScene_ConnectingProgress as a dedicated UI class.
Combines the best of two approaches: non-blocking sockets with select()
timeout and SO_RCVTIMEO clearing (prevents random disconnects) with the
upstream's state enum, FinalizeJoin separation, and ConnectingProgress UI.
JoinGame() now returns JOINGAME_PENDING on Win64, and
PlatformNetworkManagerStub::DoWork() polls the join state to finalize
the connection when the background thread succeeds.
Server list: edits and deletions now update the UI immediately by
calling SearchForGames() in ForceFriendsSessionRefresh() and
UpdateGamesList() on nav-back to LoadOrJoinMenu.
Connection: moved WinsockNetLayer::JoinGame() to a background thread
with non-blocking sockets (5s timeout, 3 retries). Users can cancel
with B/Escape during the attempt. Failed connections always show an
error dialog.