fix(auth)!: a first password takes a fresh proof of the account's way in

The fourth reading's first finding: password.set took a session alone,
so whoever took one made a GitHub-only account, or an address account
without a password, theirs for good (their address or password, their
authenticator; GitHub then refused the owner).

- An account with an address proves it anew: a code mailed to that
  address for this (EmailCodePurpose.firstPassword, its own mail), never
  the session alone, a code asked for anything else, or another address.
- An account that signs in with GitHub alone does it within 10 minutes of
  a GitHub sign-in (the session's method and creation time, where the
  session lives; members tell the register), refused signInAgain before
  any code is used; the address it adds is proved as before.
- Anonymous people still become identified with a code to the address
  they add.

The app mails the code to the person's own address (asking for it where
the device doesn't know it), offers a password right after a GitHub
sign-in (D2's "at their next sign-in") before the person's app, and asks
for a GitHub sign-in anew when the instance refuses an older one, keeping
the code typed.

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

@@ -462,5 +462,10 @@
   "passwordAddressUnknown": "Enter your account's email address: the code goes there.",
   "passwordDeleteIntroByMail": "Your account goes with everything in it, in every service of this instance. None of its authenticators works now, so a code by mail confirms it: type your password, then the code we email to your address.",
   "passwordDeleteSendCode": "Email me a code",
-  "passwordChangedSignInAgain": "Your password was changed, but this service couldn't sign you in just yet. Sign in again with the new password."
+  "passwordChangedSignInAgain": "Your password was changed, but this service couldn't sign you in just yet. Sign in again with the new password.",
+  "passwordSignInAgain": "To give an account that signs in with GitHub its password, sign in with GitHub again first: it has been more than a few minutes.",
+  "passwordSignInWithGitHubAgain": "Sign in with GitHub again",
+  "passwordOfferTitle": "Set up a password",
+  "passwordOfferBody": "Sign-in with GitHub is ending. Set up a password and an authenticator app to keep your account.",
+  "passwordOfferLater": "Later"
 }