feat(ecs): ludic.vehicles on a Table<Vehicle>

The vehicles are rows of a ludic.base Table with kind and owner as columns, every player's own by
an owner index and a nid map: vehicle_of walks only that player's rows, vehicle_by_nid is a map
lookup, and a player who leaves has their rows removed instead of the whole list rebuilt. ve_add
takes the owner, so the owner is filed once and never assigned around the table. Positions stay
on the record: a boat moves every frame and there are at most two a player. vehicles_test holds
the table (9 tests); the game builds against it and lab/unit passes (88 tests).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.vehicles/kinds.ludic

@@ -19,6 +19,8 @@ export property Vehicle {
   rider: int = -1         # the player on it, -1 nobody
   home_x: float = 0.0     # a horse is tied where its home is
   home_z: float = 0.0
+  ent: int = -1           # its handle in the table
+  tab: Table<Vehicle> = null
 }
 
 export const VEHICLE_MOUNTED: int = 0