Track becomes a deck card, Departments become decks, and trains must be made up to leave, industry restrictions enforced, update display and add a new game button

README.md

@@ -67,6 +67,9 @@ syntax**: no `enum`, no parameter properties, no namespaces. `tsconfig.json` enf
 - **State is `fold(events)`.** The event log is the source of truth, which is what gives reconnection,
   restart recovery and post-game replay from a single decision.
 - **Never call `Math.random()`.** One ambient random call silently breaks replay.
+- **Track is a deck card.** 104 of the 243 cards in the Home Office deck are track — the largest
+  category — so a district is built from what you draw, and building it costs you the industry or
+  train you drew instead. There is no separate supply and no one-piece-a-turn cap.
 - **The track is 45° geometry, not a graph on a grid.** Measured off `docs/tracks.png`: the through
   rail runs east–west across the *exact vertical middle* of every card, there is no north–south track
   anywhere, and everything that leaves through the north or south edge does so at **45°, through the