Remove registry search index

[charlesHetterich]

Summary

• remove the registry OrderedIndex and searchContractNames contract method
• remove the searchContractNames ABI entry and related registry e2e coverage
• hide the frontend home-page search bar while search is unavailable

Notes

• latest-order pagination through getContracts remains unchanged
• direct navigation to /search is intentionally left in place for now, but the search UI is no longer advertised from the home page

Verification

• pnpm format:check
• cargo fmt --check
• make build-registry
• pnpm --filter @parity/cdm-builder build
• pnpm --filter @parity/cdm-frontend build