Support ML-DSA (FIPS 204) post-quantum signature algorithms for certificate signing

France's ANSSI will [stop certifying non-PQC products from 2027](https://gizmodo.com/the-quantum-threat-to-encryption-is-coming-france-just-set-a-2027-deadline-2000773650). The US [Executive Order 14409](https://www.whitehouse.gov/presidential-actions/2026/06/securing-the-nation-against-advanced-cryptographic-attacks/) mandates PQC for all federal systems, with key establishment by 2030 and digital signatures by 2031. Australia's ASD/ACSC has published [post-quantum vendor guidance](https://www.cyber.gov.au/business-government/secure-design/quantum/post-quantum-questions-to-ask-your-vendors) urging organizations to assess PQC readiness across their supply chain.

## Context

cfssl is Cloudflare's widely used PKI toolkit for certificate signing, bundling, and verification. While Cloudflare has been a leader in deploying PQC at the network level (X25519MLKEM768 enabled across their CDN), cfssl itself has zero post-quantum algorithm support.

Organizations using cfssl to run internal CAs cannot issue ML-DSA signed certificates, even though NIST standardized ML-DSA (FIPS 204) in August 2024.

## Proposal

Add ML-DSA-44, ML-DSA-65, and ML-DSA-87 as supported key/signature types in cfssl:

1. **Key generation**: `cfssl genkey` with `-algo mldsa65` support
2. **Certificate signing**: CA signing with ML-DSA keys
3. **CSR handling**: Parse and validate ML-DSA CSRs
4. **Hybrid support**: Consider hybrid RSA+ML-DSA or ECDSA+ML-DSA certificates for transition

Go 1.27 will ship `crypto/mldsa` in stdlib. Until then, `filippo.io/mldsa` provides a bridge implementation.

## References

- [NIST FIPS 204 (ML-DSA)](https://csrc.nist.gov/pubs/fips/204/final)
- [US Executive Order 14409](https://www.whitehouse.gov/presidential-actions/2026/06/securing-the-nation-against-advanced-cryptographic-attacks/)
- [Australia ASD PQC Vendor Guidance](https://www.cyber.gov.au/business-government/secure-design/quantum/post-quantum-questions-to-ask-your-vendors)

Start at the cfssl genkey entry point and trace certificate signing and CSR parsing/validation. Compare the available Go ML-DSA implementation options, then define how ML-DSA-44, ML-DSA-65, and ML-DSA-87 are represented across those flows. Done means the requested key generation, signing, and CSR handling work, with hybrid certificate support resolved explicitly.

Written by the indexing model from the issue text.