fix(keys): new passwords have at least 12 characters

The register can't check a password it never sees, and should its
database leak, the verifier and the keys wrapped under the password fall
to guessing at Argon2id's cost (the second reading's M8). Devices now
refuse a new password shorter than 12 characters, counted as code points
once normalised (halkyon_keys' checkNewPassword), at sign-up, a reset
keeping the keys and a change alike, before anything is derived; the new
password's field says so, and the refusal has its own text (en, de).
Signing in takes any length, so a password set before keeps working.

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

@@ -756,6 +756,16 @@ class HalkyonAppLocalizationsEn extends HalkyonAppLocalizations {
   @override
   String get passwordFailed =>
       'Couldn\'t reach the instance. Check the connection and try again.';
+
+  @override
+  String passwordMinLength(int count) {
+    return 'At least $count characters';
+  }
+
+  @override
+  String passwordTooShort(int count) {
+    return 'A new password needs at least $count characters: should the instance\'s database ever leak, a short one is guessed first.';
+  }
 }
 
 /// The translations for English, as used in the United Kingdom (`en_GB`).