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_app/lib/l10n/halkyon_app_localizations_en.dart

@@ -771,6 +771,10 @@ class HalkyonAppLocalizationsEn extends HalkyonAppLocalizations {
   String passwordCodesWait(String date) {
     return 'Too many wrong codes in a row: no code is taken until $date. If they weren\'t yours, someone knows your password: change it then.';
   }
+
+  @override
+  String get passwordDeleteIntro =>
+      'Your account goes with everything in it, in every service of this instance. To confirm, type your password and a code from your authenticator app.';
 }
 
 /// The translations for English, as used in the United Kingdom (`en_GB`).