feat(bgm): add surface mounting and setup surfaces

packages/bgm/src/__fixtures__/harbor/harbor.md

@@ -46,6 +46,13 @@ type: board
 id: harbor
 role: surface
 size: [300, 200]
+mount:
+  kind: table
+  x: 0
+  y: 0
+  rotation: 0
+children:
+  - board#player
 layout:
   - route: /dock/:seat
     candidates:
@@ -56,6 +63,29 @@ layout:
     rotation: 0
 ```
 
+```yaml file=parts/player.yaml
+type: board
+id: player
+role: surface
+size: [200, 200]
+mount:
+  kind: child
+  x: 100
+  y: 50
+  rotation: 0
+layout:
+  - route: /hand/:slot
+    candidates:
+      $variants: ./hand.csv
+```
+
+```csv file=parts/hand.csv
+slot,x,y,rotation
+string,number,number,number
+0,0,0,0
+1,0,20,0
+```
+
 ```csv file=parts/seats.csv
 seat,x,y,rotation
 string,number,number,number
@@ -69,6 +99,9 @@ string,number,number,number
 role: setup
 type: game
 id: main
+surfaces:
+  - board#harbor
+  - board#player
 setup:
   /dock/0: harbor:token#wood
   /deck: harbor:token#grain