test(bgm): cover emitted shape and multi-package collection

Add a SerializedPackage type for the JSON the plugin emits, and tests
that assert the maps serialize to plain objects, that the packages module
returns every package, and that buildStart watches def files. Add a
second fixture package to exercise multi-package collection.

packages/bgm/src/__fixtures__/vite-build/games/azul/azul.md

@@ -0,0 +1,52 @@
+# Azul
+
+A second tiny example game, used to exercise the loader's collection of
+multiple packages.
+
+```yaml file=azul.yaml
+role: package
+id: azul
+title: Azul
+designer: Michael Kiesling
+players: 4
+language: en
+include: ['**/azul/**/*.yaml']
+```
+
+```yaml file=parts/tiles.yaml
+role: part
+type: tile
+id: blue
+face: ./assets/tiles.png
+faceCrop: [0, 0, 5, 5]
+size: [20, 20, 3]
+fillet: 1
+```
+
+```yaml file=parts/board.yaml
+type: board
+id: azul
+role: surface
+size: [400, 300]
+layout:
+  - route: /factory/:n
+    candidates:
+      $variants: ./factories.csv
+```
+
+```csv file=parts/factories.csv
+n,x,y,rotation
+string,number,number,number
+0,-150,0,0
+1,-50,0,0
+2,50,0,0
+3,150,0,0
+```
+
+```yaml file=setup/main.yaml
+role: setup
+type: game
+id: main
+setup:
+  /factory/0: azul:tile#blue
+```

packages/bgm/src/__fixtures__/vite-build/games/harbor/harbor.md

@@ -10,6 +10,7 @@ title: Harbor
 designer: Jane Doe
 players: 2
 language: en
+include: ['**/harbor/**/*.yaml']
 ```
 
 ```yaml file=parts/tokens.yaml

packages/bgm/src/__fixtures__/vite-build/src/main.ts

@@ -1,11 +1,13 @@
 import harbor from 'virtual:bgm/package/harbor';
+import azul from 'virtual:bgm/package/azul';
 import packages from 'virtual:bgm/packages';
 
 // Re-export the package data so the test can assert the bundled output.
-export const parts = [...harbor.parts.keys()];
-export const surfaces = [...harbor.surfaces.keys()];
-export const setups = [...harbor.setups.keys()];
+export const parts = Object.keys(harbor.parts);
+export const surfaces = Object.keys(harbor.surfaces);
+export const setups = Object.keys(harbor.setups);
 export const title = harbor.meta.title;
+export const azulTitle = azul.meta.title;
 export const allIds = packages.map((p) => p.meta.id);
 
-console.log(title, parts, surfaces, setups, allIds);
+console.log(title, parts, surfaces, setups, allIds, azulTitle);