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.
Call out that the tabletop and engine package split is not yet landed, add a status note to tabletop.md, and drop the retired WIP banner in bgm-loader.md.
Group the bgm spec cluster under docs/bgm and move dev logs and plans under docs/status, add an overview index, and update cross-references in the docs, README, and source comments.