Add folder anatomy (scripts/agent.py + references/api-reference.md) for 648 cybersecurity skills

Complete skill folder anatomy across all cybersecurity skills:
- scripts/agent.py: 80-150 line Python agents using real libraries (impacket,
  boto3, azure-mgmt-*, kubernetes, pefile, yara, scapy, shodan, stix2, etc.)
- references/api-reference.md: real API documentation with method signatures
- LICENSE: MIT license for all skill folders

skills/performing-service-account-credential-rotation/references/api-reference.md

@@ -0,0 +1,58 @@
+# API Reference: Service Account Credential Rotation
+
+## AWS IAM CLI Key Rotation
+
+| Command | Description |
+|---------|-------------|
+| `aws iam create-access-key --user-name <user>` | Create new access key |
+| `aws iam list-access-keys --user-name <user>` | List existing keys |
+| `aws iam update-access-key --access-key-id <id> --status Inactive` | Deactivate old key |
+| `aws iam delete-access-key --access-key-id <id> --user-name <user>` | Delete old key |
+
+## Azure AD CLI Credential Rotation
+
+| Command | Description |
+|---------|-------------|
+| `az ad app credential reset --id <app-id> --years 1` | Generate new client secret |
+| `az ad app credential list --id <app-id>` | List current credentials |
+| `az ad app credential delete --id <app-id> --key-id <key-id>` | Remove old credential |
+
+## HashiCorp Vault Database Secrets Engine
+
+| Endpoint | Method | Description |
+|----------|--------|-------------|
+| `/v1/database/creds/{role}` | GET | Generate dynamic database credentials |
+| `/v1/database/config/{name}` | POST | Configure database connection |
+| `/v1/database/roles/{name}` | POST | Create dynamic credential role |
+| `/v1/sys/leases/revoke` | PUT | Revoke a dynamic credential lease |
+
+### Vault Request Headers
+
+| Header | Value |
+|--------|-------|
+| `X-Vault-Token` | Vault authentication token |
+| `Content-Type` | `application/json` |
+
+## GCP Service Account Key Rotation
+
+| Command | Description |
+|---------|-------------|
+| `gcloud iam service-accounts keys create` | Create new key |
+| `gcloud iam service-accounts keys list --iam-account <sa>` | List keys |
+| `gcloud iam service-accounts keys delete <key-id>` | Delete old key |
+
+## Python Libraries
+
+| Library | Version | Purpose |
+|---------|---------|---------|
+| `subprocess` | stdlib | Execute AWS/Azure/GCP CLI commands |
+| `requests` | >=2.28 | HashiCorp Vault HTTP API calls |
+| `hvac` | >=2.1 | HashiCorp Vault Python client |
+| `boto3` | >=1.26 | AWS IAM programmatic key rotation |
+
+## References
+
+- AWS Secrets Manager Rotation: https://docs.aws.amazon.com/secretsmanager/latest/userguide/rotating-secrets.html
+- HashiCorp Vault Database Engine: https://developer.hashicorp.com/vault/docs/secrets/databases
+- Azure Key Vault Rotation: https://learn.microsoft.com/en-us/azure/key-vault/secrets/tutorial-rotation
+- GCP Key Rotation: https://cloud.google.com/iam/docs/key-rotation