Add Contract Bridge: auction, dummy play, and rubber scoring

New cg-bridge.el: a four-handed Bridge game (you are South, partnering
North against East and West) on the shared cg-game base.

* Auction: level/strain bids plus pass, double, and redouble, with the
  three-pass end rule, pass-outs, doubling state, and declarer
  determination (first of the side to name the strain).
* Play: follow-suit with the dummy exposed after the opening lead; the
  declarer plays both hands. Trick resolution honours trump and no-trump.
* Scoring: classic rubber -- trick points below the line toward game;
  overtricks, slam, insult, and undertrick penalties above; vulnerability
  and the rubber bonus. Verified against known results.
* A small natural bidding AI (openings, NT, raises with a fit, simple
  overcalls) that always terminates the auction, plus a greedy
  card-play AI.

Wire cg-bridge into the chooser, the Makefile, and the README, and add
two ERT tests (scoring math and a dozen full AI-driven deals). The suite
is now 109/109 and every file byte-compiles cleanly.

card-games.el

@@ -57,6 +57,7 @@
 (require 'cg-scopa)
 (require 'cg-trick-ext)
 (require 'cg-spite)
+(require 'cg-bridge)
 
 (defvar card-games-list
   '(("500 (Bid)" cg-bid
@@ -122,7 +123,9 @@
     ("Briscola" cg-briscola
      "Trick-taking: fixed trump, no follow; capture the points to 61.")
     ("Spite & Malice" cg-spite
-     "Climbing patience: race to empty your goal pile; Kings are wild."))
+     "Climbing patience: race to empty your goal pile; Kings are wild.")
+    ("Bridge" cg-bridge
+     "Trick-taking: the auction, the dummy, and rubber scoring, to 121."))
   "Registry of playable games.
 Each entry is (NAME COMMAND DESCRIPTION); `card-game' lists them.")