fix(visualizer): expand user path in visualizer.py (#9467)

[R1212122]

问题

修复 #9467：ppdet/utils/visualizer.py 第 112 行使用了未扩展的路径（如 ~），运行推理时会在当前目录生成 ~ 文件夹，影响用户使用。

根因

download.py 中 WEIGHTS_HOME = osp.expanduser("~/.cache/paddle/weights") 已正确展开，
但 visualizer.py 第 112 行传了未展开的 "~/.cache/paddle/" 给 get_path()。

修复

使用 os.path.expanduser() 包裹路径变量，确保用户主目录路径被正确展开。

-    font_path, _ = get_path(font_url, "~/.cache/paddle/")
+    font_path, _ = get_path(font_url, os.path.expanduser("~/.cache/paddle/"))

测试

• python -m py_compile ppdet/utils/visualizer.py 通过
• 语法检查通过
• 本地推理可视化测试（待 manual 验证）

影响

• 风险：极低（仅修改 1 行）
• 兼容性：完全向后兼容
• 性能：无影响

Checklist

• 签 CLA（CLAassistant bot 自动检测）
• 修复一个 issue
• 单行修改，PR 标题用英文 + issue 编号

[R1212122]

ping @CLAassistant

[R1212122]

I have read and agree to the PaddlePaddle Contributor License Agreement.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[R1212122]

CLA signed, please recheck