feat(account): show the account its own last sign-in

Settings → Account names the latest sign-in on any device (only the
admin's user list did, though the 0.88 notes said otherwise), and the role
in the reader's language instead of the raw `user`.

backend/app/routes/me.py

@@ -23,6 +23,7 @@ from app import logs
 from app import sysconfig
 from app.db import get_db
 from app.models import Invite, User
+from app.utils import iso
 
 router = APIRouter(prefix="/api/me", tags=["me"])
 
@@ -138,6 +139,9 @@ def get_me(
             user.google_email if user.google_email and user.google_email != user.email else None
         ),
         "has_password": user.password_hash is not None,
+        # The account's latest sign-in on any device — shown in Settings → Account, so a sign-in the
+        # user does not recognise is something they can see (null: none since 0.88, or the demo).
+        "last_login_at": iso(user.last_login_at),
         # Instance-wide: whether Google sign-in / YouTube connect is available at all (the UI hides
         # YouTube-access affordances and the onboarding nudge when it isn't configured).
         "google_enabled": google_enabled(db),