feat: add ZPan app

[saltbo]

Summary

• Add ZPan as a CapRover one-click app.
• Deploy both the ZPan web service and downloader node.
• Include the updated ZPan logo, persistent volumes, public URL setting, downloader BitTorrent port, and seed cache limit.

Validation

• Parsed public/v4/apps/zpan.yml with yq.
• Ran npm run validate_apps successfully; zpan was validated.
• Ran npm run formatter successfully.

Note: the template pins ghcr.io/saltbo/zpan:2.7.1 and ghcr.io/saltbo/zpan:2.7.1-cli because the current latest tag resolves to the downloader image config, while 2.7.1 resolves to the web service image.

[githubsaturn]

Thanks!