refactor(bgm): use doc-relative include in games and fixtures

The default include is now resolved relative to the package
declaration's directory, so the explicit root-relative patterns are
redundant. Drop them in favor of the default.

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

@@ -10,7 +10,7 @@ title: Azul
 designer: Michael Kiesling
 players: 4
 language: en
-include: ['**/azul/**/*.yaml']
+include: ['./**/*.yaml']
 ```
 
 ```yaml file=parts/tiles.yaml

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

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