configSound.qml diverges from the other config pages (no defaults support)

[Attacktive]

The Sound config page is structured differently from the Image and Movement pages, which costs it some framework integration:

• Its root is a plain Item, while the others are Page with a title: https://github.com/Attacktive/nyan-wanderer/blob/25c8379a4fb8974d015f130ede60ea73b6f7158e/package/contents/ui/config/configSound.qml#L8-L9 vs. https://github.com/Attacktive/nyan-wanderer/blob/25c8379a4fb8974d015f130ede60ea73b6f7158e/package/contents/ui/config/configImage.qml#L9-L11
• It reads plasmoid.configuration.volume / customSoundPath directly instead of using the cfg_ alias pattern the other pages use: https://github.com/Attacktive/nyan-wanderer/blob/25c8379a4fb8974d015f130ede60ea73b6f7158e/package/contents/ui/config/configSound.qml#L11-L12
• It has no cfg_volumeDefault / cfg_customSoundPathDefault, so the Sound fields do not participate in the reset-to-defaults / modified-indicator machinery the way Image and Movement do.

Suggested fix: align the Sound page with the other two — Page root, cfg_ aliases, and cfg_*Default values matching main.xml.