fix(app): no sheet is left busy by an error nothing expected

An instance's salt of another length made the device's cryptography throw
an ArgumentError, a wrapping's nonce a RangeError, and libsodium or the
keyring may throw their own; none was a refusal, so the step's error
escaped and the sheet stayed busy, which can't be closed. halkyon_keys
now checks the lengths of what comes from elsewhere before libsodium sees
it (KeyRefusal.malformed: a salt, a wrapping, a sealed key's box, a sealed
payload), the device's cryptography turns anything else into the general
failure, and so does every password cubit, the error logged by its type
alone.

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_app/test/password/data/sodium_account_crypto_test.dart

@@ -308,4 +308,28 @@ void main() {
     expect(answer.clientProof.lengthInBytes, 32);
     expect(answer.verifiesServer(ByteData(32)), isFalse);
   });
+
+  test('what an instance sends of the wrong length fails the step, never '
+      'escaping it', () async {
+    expect(
+      crypto.unlock(
+        'correct horse battery staple',
+        salt: Uint8List(15),
+        costs: account.setup.costs,
+      ),
+      failsWith(PasswordProblem.failed),
+    );
+    // After the password proved right: the instance isn't trusted.
+    final unlocked = await unlock('correct horse battery staple');
+    expect(
+      open(
+        unlocked,
+        protocol.WrappedKeys(
+          nonce: ByteData(23),
+          cipherText: account.setup.passwordKeys.cipherText,
+        ),
+      ),
+      failsWith(PasswordProblem.instanceUnproven),
+    );
+  });
 }