Add cross-search export content tests

[karilint]

Closes #757

Summary

• add direct Supertest coverage for the streamed cross-search CSV export response
• parse the CSV body in the API test and assert representative headers, filtered rows, and sorted row order
• verify the export omits the internal full_count field from the CSV output

Validation

• git diff --check
• npm run lint:backend
• npm run tsc:backend
• cd backend && DOTENV_CONFIG_PATH=../.test.env NODE_OPTIONS='-r dotenv/config' npx jest src/api-tests/crossSearch/export.test.ts --runInBand --config jest-config.js --detectOpenHandles --forceExit
• commit hook: npm run lint and npm run tsc

[karilint]

@copilot Please review this pull request.

[Copilot]

@copilot Please review this pull request.

Reviewed. No additional code changes are needed for this PR after review. Validation run results: npm run lint and npm run tsc passed; targeted export API test is currently blocked locally because the test DB is not reachable (localhost:3306) in this environment. Commit: 5b62f18.

Warning

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I tried to connect to the following addresses, but was blocked by firewall rules:

• checkpoint.prisma.io
  • Triggering command: /opt/hostedtoolcache/node/24.15.0/x64/bin/node /opt/hostedtoolcache/node/24.15.0/x64/bin/node /home/REDACTED/work/nowdatabase/nowdatabase/backend/node_modules/prisma/build/child {"product":"prisma","version":"5.22.0","cli_install_type":"local","information":"","local_timestamp":"2026-05-21T12:08:54Z","project_hash":"a620d0a8","cli_path":"/home/REDACTED/work/nowdatabase/nowdatabase/backend/node_modules/prisma/build/index.js","cli_pa (dns block)
• download.cypress.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node index.js --exec install (dns block)

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