feat(keys): halkyon_keys, an account's keys on the device

ADR 0017's step 1, on libsodium (sodium 4.1.0+1, whose build hook
compiles the libsodium 1.0.22 it ships: a C compiler and make wherever
it builds):
- Argon2id (64 MiB, 3 passes, kept with the account and never below
  that) makes a master key, which libsodium's KDF splits into SRP's
  secret (x) and the key-encryption key.
- The account's X25519 and Ed25519 key pairs, their private halves
  wrapped with XChaCha20-Poly1305 under the KEK and under the recovery
  key, bound to their public keys.
- A 24-word BIP-39 recovery phrase (the English list, MIT) and the
  recovery key derived from it.
- Data keys sealed to the account with crypto_box_seal, bound to their
  IDs; content in ADR 0002's envelope, encrypted with a data key and
  signed with Ed25519 (detached), bound to a context the caller names.
- Secrets in libsodium's guarded memory where its API takes them.
- Tests: libsodium's Argon2id known answers, BIP-39's English vectors,
  round trips and every refusal.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_keys/test/bip39_vectors.dart

@@ -0,0 +1,102 @@
+// BIP-39's English test vectors (trezor/python-mnemonic, vectors.json, MIT
+// License): the entropy and the mnemonic it makes.
+
+/// (entropy in hex, mnemonic).
+const bip39Vectors = <(String, String)>[
+  (
+    '00000000000000000000000000000000',
+    'abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about',
+  ),
+  (
+    '7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f',
+    'legal winner thank year wave sausage worth useful legal winner thank yellow',
+  ),
+  (
+    '80808080808080808080808080808080',
+    'letter advice cage absurd amount doctor acoustic avoid letter advice cage above',
+  ),
+  (
+    'ffffffffffffffffffffffffffffffff',
+    'zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo wrong',
+  ),
+  (
+    '000000000000000000000000000000000000000000000000',
+    'abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon agent',
+  ),
+  (
+    '7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f',
+    'legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal will',
+  ),
+  (
+    '808080808080808080808080808080808080808080808080',
+    'letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter always',
+  ),
+  (
+    'ffffffffffffffffffffffffffffffffffffffffffffffff',
+    'zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo when',
+  ),
+  (
+    '0000000000000000000000000000000000000000000000000000000000000000',
+    'abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon art',
+  ),
+  (
+    '7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f7f',
+    'legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth title',
+  ),
+  (
+    '8080808080808080808080808080808080808080808080808080808080808080',
+    'letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic bless',
+  ),
+  (
+    'ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff',
+    'zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo vote',
+  ),
+  (
+    '9e885d952ad362caeb4efe34a8e91bd2',
+    'ozone drill grab fiber curtain grace pudding thank cruise elder eight picnic',
+  ),
+  (
+    '6610b25967cdcca9d59875f5cb50b0ea75433311869e930b',
+    'gravity machine north sort system female filter attitude volume fold club stay feature office ecology stable narrow fog',
+  ),
+  (
+    '68a79eaca2324873eacc50cb9c6eca8cc68ea5d936f98787c60c7ebc74e6ce7c',
+    'hamster diagram private dutch cause delay private meat slide toddler razor book happy fancy gospel tennis maple dilemma loan word shrug inflict delay length',
+  ),
+  (
+    'c0ba5a8e914111210f2bd131f3d5e08d',
+    'scheme spot photo card baby mountain device kick cradle pact join borrow',
+  ),
+  (
+    '6d9be1ee6ebd27a258115aad99b7317b9c8d28b6d76431c3',
+    'horn tenant knee talent sponsor spell gate clip pulse soap slush warm silver nephew swap uncle crack brave',
+  ),
+  (
+    '9f6a2878b2520799a44ef18bc7df394e7061a224d2c33cd015b157d746869863',
+    'panda eyebrow bullet gorilla call smoke muffin taste mesh discover soft ostrich alcohol speed nation flash devote level hobby quick inner drive ghost inside',
+  ),
+  (
+    '23db8160a31d3e0dca3688ed941adbf3',
+    'cat swing flag economy stadium alone churn speed unique patch report train',
+  ),
+  (
+    '8197a4a47f0425faeaa69deebc05ca29c0a5b5cc76ceacc0',
+    'light rule cinnamon wrap drastic word pride squirrel upgrade then income fatal apart sustain crack supply proud access',
+  ),
+  (
+    '066dca1a2bb7e8a1db2832148ce9933eea0f3ac9548d793112d9a95c9407efad',
+    'all hour make first leader extend hole alien behind guard gospel lava path output census museum junior mass reopen famous sing advance salt reform',
+  ),
+  (
+    'f30f8c1da665478f49b001d94c5fc452',
+    'vessel ladder alter error federal sibling chat ability sun glass valve picture',
+  ),
+  (
+    'c10ec20dc3cd9f652c7fac2f1230f7a3c828389a14392f05',
+    'scissors invite lock maple supreme raw rapid void congress muscle digital elegant little brisk hair mango congress clump',
+  ),
+  (
+    'f585c11aec520db57dd353c69554b21a89b20fb0650966fa0a9d6f74fd989d8f',
+    'void come effort suffer camp survey warrior heavy shoot primary clutch crush open amazing screen patrol group space point ten exist slush involve unfold',
+  ),
+];