Rummy: dealer's-choice table layer

[aaylward]

Follow-up to #1608. Every rummy table becomes a dealer's-choice session: deal after deal until people leave, and the dealer picks each deal's variant. There are no match targets.

Engine

• The table holds the dealer, the deal number, standings (hands won), and the current deal with its variant.
• The dealer rotates after each deal. The first dealer is the table's opener and picks the variant with Deal.
• The dealer may choose only a variant that fits the seats (basic 2–4; gin 2 only and 500 2–4 once they land).
• If the dealer is disconnected, the choice passes to the next connected seat.
• Serde v2: a v1 row loads as a single basic deal.

Wire

• startGame carries the first variant.
• New chooseVariant{variant}: dealer only, between deals.
• View: variant, dealNumber, standings, choosing {dealer, options}.
• dealEnded carries the hand's result. gameEnded means only that the table broke up.

Stats

• Each deal is one game played/won, logged under its own variant word (rummy, gin, rummy500).
• Update the stats reader, deja, and the otel_contract pin.

UI

• A variant picker in the dealer's chair between deals, and "X is choosing…" for everyone else.
• A standings strip and an end-of-hand sheet.
• The lobby row reads "rummy · dealer's choice · now: …".

Tests

• Engine rules, including rotation, choice validity and disconnected-dealer handoff.
• Serde v1→v2 with frozen payloads.
• Mirror e2e across several deals.
• Wire goldens.
• The PG restart test between deals.
• UI picker and standings.

Basic is the only variant offered until Gin and Rummy 500 land.