The README screenshot shows a UI nostui no longer has

Noticed while reviewing #528.

`screenshot.gif`, embedded at the top of the README, is the first thing anyone sees on GitHub. Its first frame reads:

```
0.00 ticks per sec (app) 0.00 frames per sec (render)
```

Two versions out of date at once. The two-number form was replaced by "X.XX ticks per sec" earlier in this release cycle, and #528 removes the counter and its row altogether — so the gif advertises a UI element that no longer exists, in a form that already did not exist.

It is stale independently of that: the gif shows a tab labelled `Timeline`, where the code now renders `Home`.

This needs a re-recording rather than an edit, which is why #528 left it alone.

## Acceptance

- The screenshot shows the current layout: no FPS row, and the tab bar on the top line.

Open README.md and screenshot.gif to confirm the embedded asset and compare it with the acceptance criteria. Run the application using the repository's documented instructions and re-record the GIF so it shows no FPS row and a top-line tab bar. Replace screenshot.gif and verify that the README displays the updated image.

索引モデルが issue の本文から書いたものです。