feat(examples): Add Cloud KMS and HSM Integration Examples

[Dahkenangnon]

Problem

Once the Signer abstraction (Issue #29 ) is implemented, we need official examples showing integration with production key management systems.

Proposed shape

Create examples implementing the Signer interface for:

1. AWS KMS

   • Using AWS SDK for signing operations
   • Configuration and IAM setup

2. Google Cloud KMS

   • Using Google Cloud SDK
   • Service account configuration

3. Azure Key Vault

   • Using Azure SDK
   • Managed identity setup

4. HashiCorp Vault

   • Using Vault API
   • Transit secrets engine

5. PKCS#11

   • Using node-pkcs11 or similar
   • SoftHSM2 setup for testing

Structure

Each example should include:

examples/kms/
  aws-kms/
    README.md          # Setup instructions
    signer.ts          # Signer implementation
    example.ts         # Usage example
    package.json
  gcp-kms/
    ...

Keep examples outside core packages to avoid dependency bloat.

Alternatives considered (optional)

No response