fix(auth): an account with a password deletes itself only with it and a code

A session alone deleted any account, with everything encrypted under its
keys (the second reading's lows; decided by the developer: the password
and a code, as a change of password takes). account.delete now takes a
DeletionProof (the password's SRP proof for a beginChange challenge, a
TOTP or recovery code, the host the device addressed); the register
checks it (requireOwnerToDelete), a member passing it on bound to its own
host. Accounts without a password, anonymous ones among them, delete with
their session as before. In the app, deleting an account with a password
asks for it and a code in a sheet of its own; a wrong one deletes
nothing.

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_base_server/test/integration/register/member_test.dart

@@ -433,11 +433,18 @@ final class _Register implements AccountRegister {
   }) => _answer('setRecoveryKeys', () {});
 
   @override
-  Future<void> deleteAccount(Session session, UuidValue person) =>
-      _answer('deleteAccount', () {
-        deleted.add(person);
-        accounts.remove(person);
-      });
+  Future<void> deleteAccount(
+    Session session,
+    UuidValue person, {
+    DeletionProof? proof,
+  }) => _answer('deleteAccount', () {
+    deleted.add(person);
+    deletedWith.add(proof);
+    accounts.remove(person);
+  });
+
+  /// The proofs deletions came with, as the member bound them.
+  final deletedWith = <DeletionProof?>[];
 
   @override
   Future<Set<UuidValue>> knownAccounts(
@@ -831,6 +838,24 @@ void main() {
           expect(await AuthUser.db.findById(session, anna), isNotNull);
         });
 
+        test("passes the password's proof on to the register, bound to "
+            'the host the device addressed here', () async {
+          await endpoints.account.delete(
+            asBen(),
+            proof: DeletionProof(
+              challenge: const Uuid().v7obj(),
+              clientValue: ByteData(384),
+              clientProof: ByteData(32),
+              totpCode: '123456',
+              host: 'LOCALHOST',
+            ),
+          );
+
+          expect(register.deleted, [ben]);
+          expect(register.deletedWith.single?.host, testHost);
+          expect(register.deletedWith.single?.totpCode, '123456');
+        });
+
         test('of an anonymous person deletes it here alone', () async {
           await endpoints.account.delete(asAnna());