fix(git): git-status IPC returns a flat array, not wrapped object

GitOperations.getStatus returns { files: [...] } but the renderer's
ipc.file.gitStatus type declares Array<...> and calls result.data.map().
The mismatch made GitStatusPanel.tsx throw 'n.map is not a function'
on mount, which blanked the entire React tree.

Unwrap result.files in the IPC handler so it returns the array the
renderer expects. Add tests covering the success, empty, and non-git
branches so this regression cannot recur.

Refs: blank-screen-on-md-open

src/main/files/git.js

@@ -8,7 +8,8 @@ function register(currentFileRef) {
     const dir =
       rootPath ||
       (currentFileRef.current ? require('path').dirname(currentFileRef.current) : process.cwd());
-    return GitOperations.getStatus(dir);
+    const result = GitOperations.getStatus(dir);
+    return Array.isArray(result?.files) ? result.files : [];
   });
 
   ipcMain.handle('git-stage', async (_event, { rootPath, files }) => {