feat(platform): add Potato App Store v1 with official catalog and GitHub sideloading #244

Summary

Add a first Potato App Store flow so users can install optional Potato apps without copying directories manually.

For v1, keep the source model simple:

• one official GitHub app-store repo
• optional sideload by GitHub repo URL
• no third-party store ecosystem yet

Implementation requirement

This ticket must be developed TDD-first.

Scope

• Add a platform-level app store UI for browsing installable Potato apps.
• Back the official catalog with a separate GitHub repository containing one directory per app.
• Reuse the existing Potato app structure:
  • app.json
  • app directory contents
• Install flow:
  • fetch app payload from the store source
  • copy it into /opt/potato/apps/<id>/
  • make it discoverable by the existing app framework
• Uninstall flow:
  • remove the installed app directory
  • keep platform behavior clean after removal
• Add sideload support by GitHub repo URL for repos that contain a valid Potato app.
• Show enough app metadata to browse confidently:
  • name
  • description
  • icon
  • version
  • source
• Keep the platform shell responsible for install/uninstall state, not the individual apps.

Acceptance criteria

• A user can browse apps from the official Potato app catalog in the UI.
• A user can install an app from the official catalog without manual file copying.
• An installed app appears in the platform app switcher after install/reload as expected.
• A user can uninstall an installed app cleanly.
• A user can sideload an app by GitHub repo URL if that repo contains a valid Potato app.
• Invalid or unsupported repos fail with a clear error message.
• The implementation works with the existing discover_apps() / manifest-driven app lifecycle model.

Test expectations (required)

• Unit:
  • catalog parsing
  • manifest validation
  • install/uninstall path handling
  • sideload URL validation
• API:
  • list available apps
  • install app
  • uninstall app
  • sideload app
• UI/e2e:
  • browse catalog
  • install app
  • uninstall app
  • sideload valid/invalid repo
• Manual:
  • verify on a real Pi that install/uninstall/sideload work end to end

Non-goals

• Third-party store registration / multiple store sources
• Ratings, reviews, or app search beyond a basic list
• App auto-update system
• Permissions / sandboxing model
• Full marketplace moderation workflow

Related

• Builds on the existing app framework from #121 / #217
• Follows the current manifest-based app architecture already used in apps/
• Future follow-up can add third-party stores once the official-store + sideload flow is proven