[SandObserver]

Summary

• Skip the container lookup in /api/health when no socket proxy address is configured, so container-backed apps are no longer reported unhealthy.
• Omit items from the health response when neither a container nor a ping check runs for them.
• Keep the per-app health toggle interactive while Docker container health checks are off, so a URL check still works and the check can be switched off.
• Reword app.healthGlobalOff in all six catalogs to state that only container checks need the global setting.

Testing
All green. Added 2 backend tests covering the health route with no socket proxy configured.

Checklist

• Stays within the project constraints: one container, no runtime dependencies, no build step (see CONTRIBUTING.md).
• Tests added or updated for new logic, and the full suite, lint, and typechecks pass.
• Docs updated if behavior or configuration changed.
• CHANGELOG.md updated under Unreleased if the change is user-visible.