Add live multiplayer 500 over cg-net (cg-bid-net.el)

Host-authoritative networked 500: host sits South, joiners take W/N/E,
open seats filled by AI. Per-seat rotated state hides other hands and the
kitty; clients reuse the single-player renderer/commands via :around advice,
so cg-bid.el/cg-bid-ui.el are untouched. Adds cg-bid-host/cg-bid-join, a
start-now lobby with auto-start at four players, and cg-bid-shuffle-partners.
cg-net.el gains cg-net-connect-functions. Verified: clean byte-compile,
checkdoc, 34/34 ERT (incl. 3 new net tests) and a two-process TCP game.

card-games.el

@@ -43,6 +43,7 @@
 (require 'cg-net)
 (require 'cg-gaps)
 (require 'cg-bid-ui)
+(require 'cg-bid-net)
 
 (defvar card-games-list
   '(("500 (Bid)" cg-bid