feat(admin): add exam operations detail

[coding-hui]

Summary

• Add Batch 3 exam operations metadata to admin exam detail responses, including snapshot, scoring, candidate, submission, result, and audit counts.
• Convert exam sessions to paginated admin responses and update the ExamDetail tables to request page/page_size from ProTable pagination.
• Add an operations header to ExamDetail and preserve the active detail tab in the URL.
• Mark Batch 3 complete in the roadmap plan.

Impact

Admin exam detail now behaves like an operations console instead of fixed 100-row loads. Operators can inspect snapshot context and live counts while paging users, submissions, and audit events without loading all rows at once.

Verification

• go test ./...
• go test ./internal/api ./internal/exam
• pnpm --dir apps/admin jest --runInBand
• pnpm --dir apps/admin lint
• pnpm --dir apps/admin build
• git diff --check
• Chrome regression for operations header fields, results/sessions/events paginated requests, tab URL persistence, and console cleanliness.

[chatgpt-codex-connector]

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