feat(tabletop): add free-interaction layer (layer 3)

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.

docs/bgm/interactions.md

@@ -5,9 +5,10 @@ with a bgm game that has no rules yet: a sandbox. It builds on the state model:
 see [`state-model.md`](./state-model.md) for components-vs-setup, path→stack ×
 facing, and the anchoring scope.
 
-> **Status:** Design. Proposes the operation set, the command/dialog split, and
-> the deck-pick-up dialog before the interaction half of `@tts/tabletop` is
-> built.
+> **Status:** Implemented (layer 3, sandbox). The operation set, the
+> command/dialog split, and the deck-pick-up dialog are built in
+> `@tts/tabletop` (`interactions.ts`, `dialog.tsx`). Rule-enforced play (layer
+> 4) is not yet wired — the rule seam is a no-op filter over free interaction.
 
 ## 1. The operation set is closed and tiny