refactor(core,keys): BIP-39's English list moves into halkyon_core

The list a recovery phrase's words are of moves from halkyon_keys into
halkyon_core, exported as bip39English, so that the server module can
take a waiting account's matching code from it (Halkyon Learn's ADR
0021, D33) without depending on halkyon_keys and libsodium. Its test
(2048 words, sorted, the published file's SHA-256, unique by their first
four letters) moves along; its MIT licence too.

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_core/pubspec.yaml

@@ -12,4 +12,6 @@ dependencies:
   uuid: ^4.5.0
 
 dev_dependencies:
+  # SHA-256, which the BIP-39 list is checked against.
+  crypto: ^3.0.7
   test: ^1.25.0