Replace inline loading spinners with the shared LoadingPage #1980

Summary

Replace the inline loading spinner with the shared LoadingPage, which already exists in
@tumaet/prompt-ui-components (and is already used by some files). No dependency; pure find/replace.

What is duplicated (verified, 31 occurrences across all 7 phase components + core)

<div className='flex justify-center items-center h-64'><Loader2 className='h-12 w-12 animate-spin text-primary'/></div>:

• clients/example_component/src/example_component/pages/SettingsPage.tsx:27
• clients/certificate_component/src/certificate/pages/ParticipantsPage.tsx:146
• clients/matching_component/src/matching/MatchingOverviewPage.tsx:56
• clients/interview_component/src/interview/pages/InterviewDataShell.tsx

Work

• Swap each inline block for <LoadingPage />.