Frontend: add missing component spec files (5 components)

[pcastelo]

Problem

5 of 15 frontend components have zero spec files. Only migration-wizard, app-shell, and shared UI have tests.

Missing spec files

• features/dashboard/dashboard.component.spec.ts — data loading, cluster status display
• features/chat/chat.component.spec.ts — message send/receive, markdown rendering, error states
• features/audit/audit-log.component.spec.ts — log listing, filtering, pagination
• features/settings/settings.component.spec.ts — source/cluster CRUD, form validation
• features/threescale-explorer/threescale-explorer.component.spec.ts — product listing, backend mapping

Acceptance criteria

• One spec file per component above
• Test component creation, data binding, user interactions
• Mock API services (use HttpClientTestingModule)
• Test error states and loading states
• Minimum 3 test cases per component