Add platform health dashboard

[andreasohlund]

Summary

• add the first in-app Platform health page, nav item, support modal, and dev-mock controls
• introduce a shared frontend platform model used by Platform health and Platform Capabilities
• align dashboard capability status badges with Platform health navigation, add status-specific nav tooltips, link platform health instance names to their API URLs, remove duplicated instance widgets from capability cards, and remove footer ServiceControl/Monitoring widgets

Design decisions

• Use a shared frontend platform model/store as the source of truth for both Platform health and Platform Capabilities.
• Keep Platform health focused on instance and topology visibility, not configuration-readiness guidance.
• PlatformModel.monitoring remains PlatformInstance | null and is shared by both Platform health and Platform Capabilities.
• Do not model the multi-region concept explicitly in the shared frontend model; derive the needed behavior from instance roles instead (primary-error, remote-error, remote-audit, monitoring).
• Keep PlatformHealthRow page-specific rather than pushing table-only display semantics into the shared model.
• Keep the implementation frontend-only and mock-driven; do not introduce a new ServicePulse backend endpoint in this PR.
• In Platform Capabilities, show grey Not configured badges for instance-not-configured states and keep capability-specific readiness semantics there.
• Remove per-instance widgets from Platform Capabilities cards so instance-level visibility lives on the Platform health page, while capability-specific widgets such as Messages and Metrics stay on the cards.
• Platform health nav icon precedence is danger > warning > info for outdated-only cases, and the menu item tooltip follows the same status precedence.
• Platform health instance names link directly to each instance apiUrl from the shared platform model.

Keep this section up to date as implementation and product decisions evolve.

Test scenarios

Use cd src/Frontend && VITE_MOCK_SCENARIO=<name> npm run dev:mocks.

Startup scenarios:

• platform-health
• platform-health-outdated

Then switch live in the browser console with window.__platformHealth.setScenario(...):

• single-region-healthy
• single-region-warning: monitoring healthy, one degraded audit instance
• single-region-danger
• single-region-outdated
• multi-region-healthy
• multi-region-warning
• multi-region-danger: remote error unavailable, no monitoring

Runtime helpers:

• window.__platformHealth.getState()
• window.__platformHealth.reset()
• window.__platformHealth.setStatus('primary' | 'monitoring' | 'remote-0' | 'remote-1', 'healthy' | 'degraded' | 'unavailable')
• window.__platformHealth.setWarnings([...])
• window.__platformHealth.clearWarnings()

[andreasohlund]

Not sure about this one, needs disussion

[andreasohlund]

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