feat(admin): harden content asset workflow

[coding-hui]

Summary

• Block published questions from being unpublished while they are referenced by published papers.
• Require programming questions to have at least one sample test case and one hidden test case before publish.
• Add backend coverage for dependency-safe batch status actions and mark Batch 2 complete in the implementation plan.

Impact

Admins now receive per-item batch status results with clear backend reasons when content asset actions are blocked. Published papers remain protected from silently referencing unpublished questions.

Verification

• go test ./...
• go test ./internal/library ./internal/api
• pnpm --dir apps/admin jest --runInBand
• pnpm --dir apps/admin lint
• pnpm --dir apps/admin build
• Chrome regression for batch status partial failure, programming publish readiness, paper detail save-bar readiness summary, and migrated legacy 404 routes.

[chatgpt-codex-connector]

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