feat: Add ML-KEM-768 (FIPS 203) post-quantum KEM support

Integrates mlkem-native (Apache-2.0/MIT/ISC) for ML-KEM-768 key
encapsulation on the OnlyKey hardware token.

New capabilities:
- ML-KEM-768 keypair generation (KEYTYPE_MLKEM768 = 5)
- ML-KEM-768 decapsulation (recover shared secret from ciphertext)
- ML-KEM-768 public key retrieval from stored keypair

Implementation details:
- Uses mlkem-native v1.0.0 C-only portable backend (no assembly)
- All C code is CBMC-verified memory-safe
- RNG bridged to ArduinoLibs RNG.rand() via MLK_CONFIG_CUSTOM_RANDOMBYTES
- Secret key (2400 bytes) stored AES-GCM encrypted in flash sectors 10-11
  (repurposed from FIDO2 resident key slots 5-8)
- Runtime scratch uses existing ctap_buffer (no new static allocations)
- PACKET_BUFFER_SIZE bumped 768->1088 for ML-KEM ciphertext transport
- LARGE_BUFFER_SIZE bumped 1024->1088 (no extra RAM, shifts within ctap_buffer)
- Total new RAM cost: 320 bytes

Protocol:
- Keygen:  OKGENKEY    slot=133 -> returns PK (1184 bytes)
- Get PK:  OKGETPUBKEY slot=133 -> returns PK (1184 bytes)
- Decaps:  OKDECRYPT   slot=133, payload=CT (1088 bytes) -> returns SS (32 bytes)

Files added:
- mlkem_native/ - mlkem-native library (C90, FIPS 203 compliant)

Files modified:
- onlykey/okcore.h   - KEYTYPE_MLKEM768, size defines, buffer size bumps
- onlykey/okcore.cpp - Flash storage for ML-KEM secret key
- onlykey/okcrypto.h - ML-KEM function declarations
- onlykey/okcrypto.cpp - ML-KEM operations and dispatch hooks

Author: cr7pt0

.gitignore

@@ -46,3 +46,4 @@ Network Trash Folder
 Temporary Items
 .apdisk
 .vscode/settings.json
+mlkem_native/test/test_mlkem768

licenses.md

@@ -19,6 +19,17 @@ at your option.
 https://github.com/trustcrypto/libraries/blob/master/mbedtls-2.4.0/apache-2.0.txt
 https://www.apache.org/licenses/LICENSE-2.0
 
+## mlkem-native (ML-KEM / FIPS 203)
+https://github.com/pq-code-package/mlkem-native
+
+Licensed under your choice of:
+
+Apache License, Version 2.0 (http://www.apache.org/licenses/LICENSE-2.0)
+ISC License (https://opensource.org/licenses/ISC)
+MIT License (https://opensource.org/licenses/MIT)
+
+Post-Quantum Cryptography Alliance, a project of the Linux Foundation.
+
 ## Base64, Sha1, Sha256
 
 https://github.com/B-Con/crypto-algorithms