feat(app): an authenticator's key copied, marked sensitive, and its code six digits

A phone without a camera whose authenticator doesn't open otpauth: had no
way but typing the key. It is copied again, the key alone (ADR 0017
amended, the developer's decision of 3 Nov 2026): on Android through each
app's SensitiveClipboard.kt, marked EXTRA_IS_SENSITIVE, so Gboard and the
system show no preview and keep it out of their histories; elsewhere through
Flutter's clipboard. Emptied 60 seconds later if the clipboard still holds
it. The recovery phrase and codes stay never copied.

The code's field counted "/7", taking an optional space for a seventh
character: it now takes six digits alone, a pasted space dropped, and counts
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_de.arb

@@ -126,6 +126,7 @@
   "passwordAuthenticatorTitle": "Authenticator einrichten",
   "passwordAuthenticatorIntro": "Jede Anmeldung braucht einen Code aus einer Authenticator-App wie Aegis, 2FAS oder Proton Authenticator. Scanne diesen Code damit oder tippe den Schlüssel ein.",
   "passwordAuthenticatorKey": "Schlüssel",
+  "passwordAuthenticatorKeyCopied": "Schlüssel kopiert. In einer Minute wird er aus der Zwischenablage entfernt.",
   "passwordAuthenticatorOpen": "In deiner Authenticator-App öffnen",
   "passwordAuthenticatorNoApp": "Keine App auf diesem Gerät öffnet ihn. Scanne den Code oder tippe den Schlüssel ein.",
   "passwordAuthenticatorCodeIntro": "Gib dann den Code ein, den sie zeigt.",