Add cribbage for two, three or four players

The whole game: the crib, the cut, the play and the show, pegging on a
board drawn with both pegs so the last score is visible as well as the
total.

Three tables rather than one. Two play head to head with six cards and
lay two away; three play singly with five and lay one, with a fourth
card dealt straight into the crib because three hands cannot fill it;
four play in partnerships pegging on one score, where your partner's
crib is your crib. Every table keeps four cards and every crib holds
four, which is what lets one engine serve all three.

The rule that shapes the code is that a game ends on the point that
reaches the target, mid-count if that is where it falls. Every award
goes through one function that stops the game there and refuses
everything after it, so a non-dealer who counts out wins before the
dealer's hand and crib are counted at all — the show reports those as
never counted rather than adding them on.

A go is called by the engine rather than tapped. The count only rises
within a series, so a hand that cannot play now cannot play later in
it, and there is nothing to decide; the log says who went past.

The opponent works out its lay-away rather than guessing: every way of
keeping four is scored against all forty-six cards that could still be
cut, and what goes to the crib is valued separately and added or
subtracted depending on whose crib it is. It takes 114 games out of 120
against random legal play, from either seat.

teamForSeat now takes the seat count, because cribbage is only a
partnership game at four — reading seat % 2 at a table of three would
have put the first and third players on the same side.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01DCuRESmSZeJoJond43itw2

docs/RULES-cribbage.md

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+# Cribbage — implemented rules
+
+This is the ruleset the engine enforces. Anything marked **toggle** is in the
+game setup screen.
+
+## Table
+
+- 2, 3 or 4 players — **toggle**.
+  - **Two** play head to head, six cards each, laying two away.
+  - **Three** play singly, five cards each, laying one away — and a fourth card
+    is dealt straight into the crib, which is the only way three hands can fill
+    it.
+  - **Four** play in partnerships, sitting across from each other. Five cards
+    each, one away, and **the two partners peg on one score**: your partner's
+    crib is your crib, and their points are yours.
+- One 52-card deck. The deal moves one seat to the left each hand.
+- Game to **121** — twice round the board — or **61** — once — **toggle**.
+
+Whatever the table, everybody keeps four cards and the crib holds four.
+
+## The cut
+
+Once everyone has laid away, the starter is cut and turned up. It belongs to
+every hand and to the crib at the show.
+
+**A jack turned is two for his heels**, and they are the dealer's however the
+cut fell.
+
+## The play
+
+Starting at the dealer's left, cards are laid down one at a time and the count
+runs up towards **thirty-one, which it may never pass**. A card that would take
+it past cannot be played.
+
+Scored as the card lands:
+
+| | |
+| --- | --- |
+| Count reaches fifteen | 2 |
+| Count reaches thirty-one | 2 |
+| Pair | 2 |
+| Third of a rank (pair royal) | 6 |
+| Fourth of a rank (double pair royal) | 12 |
+| Run of three or more | 1 a card |
+
+Pairs and runs are read off the **end of the cards on the table**, so a pair
+split by somebody else's card is not a pair, and a run counts however jumbled
+the order it was laid in — 5, 3, 4 is a run of three.
+
+**A player who cannot play says go**, and the table plays past them. When
+nobody can play at all, whoever laid the last card takes **one for the last
+card**, the count is cleared, and the seat after them starts the next one.
+Thirty-one has already paid two, so no extra point is taken for it.
+
+A go is called by the engine rather than tapped: the count only ever rises
+within a series, so a hand that cannot play now cannot play later in it either,
+and there is nothing to decide.
+
+## The show
+
+The hands are counted **from the dealer's left, round to the dealer, and the
+dealer's crib last of all**. Each hand is its four cards plus the starter.
+
+| | |
+| --- | --- |
+| Each combination of cards adding to fifteen | 2 |
+| Each pair | 2 |
+| Each run of three or more | 1 a card |
+| Four cards of one suit in hand | 4 |
+| …with the starter matching | 5 |
+| Jack in hand of the starter's suit (his nob) | 1 |
+
+Duplicated ranks multiply runs rather than lengthening them: 4-5-5-6 is **two
+runs of three**, not a run of four.
+
+**A crib takes nothing for four of a suit.** It scores a flush only when all
+five cards, starter included, share one — the one rule that makes counting a
+crib different from counting a hand.
+
+The best hand in the game is twenty-nine: three fives and the jack of the suit
+that is cut, with the fourth five as the starter.
+
+## Winning
+
+**The game ends on the point that reaches the target, mid-count if that is
+where it falls.** A non-dealer who can count out has won before the dealer's
+hand and crib are ever counted, and the table says so — hands the game never
+got to are shown with what they would have been worth, greyed out rather than
+added on.
+
+**Skunks** — **toggle**, on by default. A loser left on the second street is
+skunked, and one who never left the first is double skunked. In a game to 121
+those lines are 91 and 61. It is a way of describing the result, not extra
+points.
+
+## What is not here
+
+- **Muggins.** Points missed at the show cannot be claimed by an opponent,
+  because they are never missed: the engine counts every hand in full. The rule
+  exists to punish bad arithmetic, and there is none to punish.
+- **The five-card game.** The old two-handed game — five cards each, a crib of
+  four, three for last, game to 61 — is a different game rather than an option,
+  and this is the six-card one.
+- **Cutting for the deal.** Seat 0 deals the first hand and the deal moves left
+  from there.
+
+## What the computer opponent does
+
+The lay-away is worked out rather than guessed. For every way of keeping four,
+it scores that hand against **all forty-six cards that could still be cut** and
+compares the averages. What goes to the crib is valued separately and then
+added or subtracted depending on whose crib it is — a five, a pair or a fifteen
+laid away is a gift to your own crib and a present to the other side's. At four
+players your partner's crib counts as your own.
+
+In the play it takes the points on offer, and otherwise tries not to leave the
+count at five or twenty-one, where any of the sixteen ten-cards collects fifteen
+or thirty-one. It will not lead a five for the same reason.