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>

docs/adr/0017-password-totp-and-keys.md

@@ -584,6 +584,17 @@ keychain on 21 Oct; the 30-day grace for GitHub-only accounts was proposed and k
 - **The clipboard (medium):** copies reached clipboard histories and cloud clipboards,
   and Android often couldn't empty it again. Nothing secret is copied any more: codes
   are saved, like the phrase; an authenticator's key is scanned, opened or typed.
+  *Amended 3 Nov 2026 (the developer):* a phone without a camera whose authenticator
+  doesn't open `otpauth:` had no way but typing, so the key alone is copied again
+  (`PlatformSecretClipboard`): on Android through each app's `SensitiveClipboard.kt`,
+  marked `EXTRA_IS_SENSITIVE` (no preview, kept out of Gboard's and the system's
+  histories); elsewhere through Flutter's clipboard, which has no mark (Windows' and
+  KDE's histories may keep it). Either way emptied 60 seconds later if it still holds
+  the key, which Android allows only while the app is in front. Alternatives weighed:
+  phones only (the desktop stays type-only), and keeping it uncopyable with the key in
+  groups of four. The phrase and the recovery codes stay never copied. The code's
+  field takes six digits alone, a pasted space dropped, without a counter (it read
+  "/7", taking the space as a seventh).
 - **Saving (medium-low):** a saved file was made, then set to 0600, and written into
   whatever the path held. Now a new file beside it, 0600 as it is made (`O_EXCL`,
   `O_NOFOLLOW`), written through its descriptor and renamed over the path; a symbolic