Consolidate platform capability status checks into PlatformCapabilitiesStore

[johnsimons]

Refactors the auditing and monitoring status checks to use a single auto-refresh mechanism. This moves the state and logic for hasSuccessfulMessages and hasMonitoredEndpoints out of their respective stores and into the PlatformCapabilitiesStore, reducing the number of concurrent refresh timers. Additionally, introduces a dedicated AuditClient to encapsulate audit-related API requests.

This PR fixes:

• All messages screen doesn't show any messages #2883

Reviewer Checklist

• Components are broken down into sensible and maintainable sub-components.
• Styles are scoped to the component using it. If multiple components need to share CSS, then a .css file is created containing the shared CSS and imported into component scoped style sections.
• Naming is consistent with existing code, and adequately describes the component or function being introduced
• Only functions utilizing Vue state or lifecycle hooks are named as composables (i.e. starting with 'use');
• No module-level state is being introduced. If so, request the PR author to move the state to the corresponding Pinia store.

[warwickschroeder]

Could we document these patterns and place in the docs folder? Additionally are there any lint rules or tests we could write to prevent issues like the one thats linked?

[dvdstelt]

This definitely does NOT fix:

• All messages screen doesn't show any messages #2883

It does fix issues, but we still need:

• Prevent isRefreshing from getting permanently stuck on fetch errors #2879