Re-add Downloads badge to all 5 READMEs once pepy.tech stats populate

[kmadan]

Goal

The Downloads badge was temporarily removed in #59 because pepy.tech and shields.io's PyPI-downloads endpoints both return red "not found" / "package not found" text for the first 24–48 hours after a fresh PyPI release. We want it back once the stats start flowing.

When to do this

Verify the badge works before adding it back:

```bash
curl https://img.shields.io/pepy/dt/aicertify.json
```

If the response no longer says "color":"red" / "message":"not found" and instead shows a real number, the badge is safe to re-add.

Where to add it

In each of the 5 READMEs, insert this line right after the PyPI badge line in the badge row:

```html

```

Files:

• README.md
• README.zh-CN.md — use alt="下载量"
• README.ja-JP.md — use alt="ダウンロード"
• README.ko-KR.md — use alt="다운로드"
• README.hi-IN.md — use alt="Downloads"

Acceptance criteria

• curl https://img.shields.io/pepy/dt/aicertify.json returns a non-red colour and a real download count
• Badge added back to all 5 READMEs
• Badge renders cleanly on the GitHub repo home page

Context

Removed in #59 (2026-05-14). See that PR for the colour-grading reasoning behind the broader badge-row tightening.