Adds age v1.3.0 plugin support for OnlyKey hardware tokens with
X-Wing hybrid KEM (draft-connolly-cfrg-xwing-kem-09).

New subpackage: onlykey/age_plugin/
- cli.py      - Plugin entry point, Bech32 encoding, key management
- protocol.py - age plugin state machine (C2SP spec, recipient-v1/identity-v1)
- onlykey_hid.py - OnlyKeyPQ class wrapping OnlyKey client for PQ slots
- xwing.py    - X-Wing combiner, HPKE key schedule (ChaCha20-Poly1305)
- mlkem_py.py - ML-KEM-768 host-side encaps via kyber-py (FIPS 203)

New console_scripts entry point: age-plugin-onlykey
New extras_require[age]: cryptography, kyber-py

Usage:
  pip install onlykey[age]
  age-plugin-onlykey --generate > onlykey-identity.txt
  age -r age1onlykey1<pk> -e secret.txt > secret.age
  age -d -i onlykey-identity.txt secret.age > secret.txt

Private key never leaves the OnlyKey device.

- Add MLKEM768(5) and XWING(6) to KeyTypeEnum
- Add CURVE25519(4) to KeyTypeEnum (was missing)
- Add 'm' (ML-KEM) and 'w' (X-Wing) type mappings in setkey()
- Allow genkey with types 'm' and 'w' in both direct and interactive CLI

Usage:
  onlykey-cli genkey ECC1 w d   # Generate X-Wing seed in ECC slot 1
  onlykey-cli genkey ECC2 m d   # Generate ML-KEM seed in ECC slot 2