fix(auth): a member deletes nobody while the register is out of reach

A person still anonymous on a member was deleted there on the session
alone while the register was out of reach (the reading of the fixes' B1).
But the register may have linked them while their becoming identified on
the member failed, so with both failing, an account of the register's went
without its proof (the short reading's L2). A member now refuses every
deletion while it can't ask the register (decided by the developer on
21 Oct).

In the app, signing out of an anonymous account, which deletes it, signs
the device out all the same when the deletion fails, as a switch already
leaves one behind: the account is left to the instance's pruning of
anonymous accounts unused for 90 days. signInWays gets its doc comment
back.

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/auth/data/auth_repository_test.dart

@@ -46,6 +46,26 @@ void main() {
       },
     );
 
+    test(
+      'gives an anonymous account up all the same when deleting it fails, '
+      'as while the register is out of reach: the device signs out, the '
+      'account left to the pruning (the short reading, L2)',
+      () async {
+        final gateway = FakeAuthGateway(
+          status: const SignedIn(
+            authUserId: 'anonymous-1',
+            isIdentified: false,
+          ),
+        )..deletionError = Exception('Internal server error');
+
+        await AuthRepository(gateway, MemorySignInAddresses()).signOut();
+
+        expect(gateway.accountDeletions, 1);
+        expect(gateway.signOuts, 1);
+        expect(gateway.status, const SignedOut());
+      },
+    );
+
     test('only signs an identified person out on this device', () async {
       final gateway = FakeAuthGateway(
         status: const SignedIn(authUserId: 'github-1', isIdentified: true),