Add the interaction half of the sandbox: a held part and dialog stack as
UI state outside the game store, with pure helpers (interactionsFor,
dropPaths, pickPath, partFacings, nextFacing). PartPlacement is now
interactive (pick up, drag to move, click to cycle facing), and a drop on
a path with a stack-dialog interaction opens the deck dialog instead of
moving directly. DialogLayer renders the stack-inspector dialog whose
insert button issues a move. Add the dialog role, Setup.interactions, and
Package.dialogs to @tts/bgm, and declare the deck insert dialog in
games/poker.
hyper