Complete folder anatomy for all 649 cybersecurity skills + update LICENSE to Mahipal

- Add scripts/agent.py and references/api-reference.md to all remaining skills
- Update all 648 LICENSE files: copyright now reads 'Mahipal'
- Add implementing-security-monitoring-with-datadog (new skill with full anatomy)
- All 649 skills now have: SKILL.md, LICENSE, scripts/agent.py, references/api-reference.md

skills/implementing-end-to-end-encryption-for-messaging/references/api-reference.md

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+# API Reference — Implementing End-to-End Encryption for Messaging
+
+## Libraries Used
+- **cryptography**: X25519 key exchange, HKDF key derivation, AES-256-GCM encryption
+
+## CLI Interface
+
+```
+python agent.py keygen                                    # Generate X25519 key pair
+python agent.py exchange                                  # Simulate key exchange
+python agent.py demo                                      # Full E2EE demo flow
+python agent.py encrypt --message <text> --key <hex>      # Encrypt message
+python agent.py decrypt --nonce <hex> --ciphertext <hex> --key <hex>
+```
+
+## Core Functions
+
+### `generate_keypair()`
+Generates X25519 key pair for Diffie-Hellman key exchange.
+- `X25519PrivateKey.generate()` -> private key
+- `private_key.public_key()` -> public key
+- Returns hex-encoded private and public keys.
+
+### `derive_shared_secret(my_private_hex, their_public_hex)`
+Performs X25519 ECDH key exchange and derives symmetric key via HKDF-SHA256.
+- `my_private.exchange(their_public)` -> 32-byte raw shared secret
+- `HKDF(algorithm=SHA256(), length=32, info=b"e2ee-messaging-v1").derive(shared)`
+
+### `encrypt_message(message, shared_key_hex)`
+Encrypts plaintext using AES-256-GCM with random 12-byte nonce.
+- `AESGCM(key).encrypt(nonce, plaintext, None)` -> ciphertext with GCM tag
+
+### `decrypt_message(nonce_hex, ciphertext_hex, shared_key_hex)`
+Decrypts and authenticates ciphertext. Raises `InvalidTag` if tampered.
+
+## Cryptography API Calls
+
+| Class | Module | Purpose |
+|-------|--------|---------|
+| `X25519PrivateKey` | `cryptography.hazmat.primitives.asymmetric.x25519` | ECDH private key |
+| `X25519PublicKey` | same | ECDH public key |
+| `AESGCM` | `cryptography.hazmat.primitives.ciphers.aead` | Authenticated encryption |
+| `HKDF` | `cryptography.hazmat.primitives.kdf.hkdf` | Key derivation |
+
+## Dependencies
+```
+pip install cryptography>=41.0
+```