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_en.arb

@@ -413,6 +413,10 @@
   "passwordAuthenticatorTitle": "Set up an authenticator",
   "passwordAuthenticatorIntro": "Every sign-in takes a code from an authenticator app, such as Aegis, 2FAS or Proton Authenticator. Scan this code with it, or type in the key.",
   "passwordAuthenticatorKey": "Key",
+  "passwordAuthenticatorKeyCopied": "Key copied. It's taken off the clipboard again in a minute.",
+  "@passwordAuthenticatorKeyCopied": {
+    "description": "After the authenticator's key was copied during its setup; the app empties the clipboard 60 seconds later."
+  },
   "passwordAuthenticatorOpen": "Open in your authenticator app",
   "passwordAuthenticatorNoApp": "No app on this device opens it. Scan the code or type in the key.",
   "passwordAuthenticatorCodeIntro": "Then enter the code it shows.",