fix(bgm): hot-reload markdown definition edits

Normalize the games root to POSIX separators so the HMR path guard
matches on Windows, and watch the real on-disk markdown files (which
defMap.files omits in favor of their virtual code blocks) so edits
trigger a re-collect instead of a manual restart.

packages/bgm/src/vite.unit.test.ts

@@ -85,10 +85,13 @@ describe('bgm vite plugin', () => {
     (plugin.buildStart as Callable<typeof plugin.buildStart>).call(context, {} as never);
 
     // Every def file (real + virtual code blocks) is watched so edits
-    // trigger a re-collect.
+    // trigger a re-collect. The real markdown source must be watched too:
+    // `defMap.files` only lists virtual code-block files, so without watching
+    // the on-disk `.md` file the dev server would never notice an edit.
     expect(watched.length).toBeGreaterThan(0);
     expect(watched.some((f) => f.endsWith('.yaml'))).toBe(true);
     expect(watched.some((f) => f.endsWith('.csv'))).toBe(true);
+    expect(watched.some((f) => f.endsWith('.md'))).toBe(true);
     expect(watched.every((f) => path.isAbsolute(f))).toBe(true);
   });
 });