Redesign record-game flow (stepped entry) — behavioral

[b006n97]

Rework game entry (CreateGame, Game, and the legacy jp/hk game screens) onto a stepped UI with clearer per-round requirements, and consolidate create routing:

• StepSection / RoundRequirements / TransactionTypeSelector (replacing TransactionTypeButtonList) / PlayerScoreCard drive the new entry flow; Footer, PlayerButtonRow, PointsInput, DropdownInput, TableDisplay restyled.
• App.tsx: /games/create/{jp,hk}[/casual] collapse to a single query-param /games/create page; legacy URLs redirect carrying variant/type.

BEHAVIORAL CHANGES (intentional, confirmed):

• constants.ts default hand: JP_UNDEFINED_HAND {han:-2,fu:10} -> {han:1,fu:30}; HK_UNDEFINED_HAND (-1) renamed/retuned to HK_DEFAULT_HAND (3). Entry now starts from a valid minimum hand instead of a sentinel.
• assignRoundAction centralizes role-exclusivity (a player can't be winner and loser at once) across every assignment path.
• getUnmet{Japanese,HongKong}RoundRequirements add soft, non-throwing validation so the UI can gate Submit; the throwing validators remain the submit-time safety net.

TESTING GAP: assignRoundAction / isValidHand / getUnmet*RoundRequirements are pure and unit-testable, but the frontend has no test runner configured. Cover via a follow-up (add vitest to frontend) or manual QA of deal-in / self-draw / pao / nagashi / deck-out entry in both variants before release.