Add platform health dashboard

[andreasohlund]

Summary

• add the Platform health page, support export, and runtime mock controls
• share one frontend platform model across Platform health and Platform Capabilities
• hide internal platform custom checks by default and let Platform health use them as secondary health signals
• map matching failing internal checks to degraded platform instances
• refresh the Platform health and Custom Checks docs to match the new behavior

Design Decisions

• Use a shared frontend platform model/store as the source of truth for Platform health and Platform Capabilities. PlatformModelStore owns normalization for primary ServiceControl, remote instances, and Monitoring, while transport stays in the purpose-specific clients.
• Keep ServicePulse as a frontend-owned model with only the fields needed for Platform health and update visibility.
• Derive topology behavior from shared instance roles instead of introducing another topology layer. Remote instances remain model-derived rows, and the direct-access rule stays limited to primary ServiceControl and Monitoring.
• Read the primary version from the real X-Particular-Version response header and the Monitoring version from its root version field. A successful primary root fetch still maps to a healthy baseline.
• Use the ServiceControl internal flag as the source of truth for platform custom checks. Older responses without the flag are treated as non-internal.
• Keep internal platform custom check inference page-specific in PlatformHealthStore. Matching is by originating_endpoint.name, and a failing internal check degrades the matching healthy instance.
• Keep PlatformHealthStore responsible for page-specific severity, rows, upgrade cues, details, and support export content, while CustomChecksStore only controls filtering and pagination for the list view.

Behavior

• Show platform custom checks reveals internal checks in the Custom Checks UI
• Platform health matches internal checks by originating_endpoint.name
• matching failing internal checks degrade the associated platform instance

Verification

• npm run test:component -- src/stores/CustomChecksStore.spec.ts src/stores/PlatformHealthStore.spec.ts test/mocks/platform-health-state.spec.ts
• npm run lint
• npm run type-check

[andreasohlund]

Not sure about this one, needs disussion

[andreasohlund]

Needs discussion: should we move this to the health page as well?

[andreasohlund]

@rbev @jpalac this should be ready for a first review pass to catch bigger mistakes, I've tried to capture all important stuff in the PR description

[andreasohlund]

Needs discussion, more stuff could go in here in the future