v0.31.3: admin Users "Last seen" = Never for unclaimed invites

An admin-created invite row showed a Last-seen timestamp identical to
Signed-up, implying the invitee had visited. users.last_seen_at is
NOT NULL DEFAULT (datetime('now')) and the invite INSERT sets neither
timestamp, so both default to row-creation time; last_seen_at only
advances on real authentication. An unclaimed invite has provably never
authenticated (the unclaimed state drives the PENDING INVITE badge), so
the Users tab now renders "Never" for the Last-seen cell of a pending
row. Signed-up (invite-created date) unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/Admin.jsx

@@ -326,7 +326,14 @@ function UserRow({ user: u, busy, onChangeRole, onToggleMute, onFlipPermission }
           )}
         </td>
         <TimeCell value={u.created_at} />
-        <TimeCell value={u.last_seen_at} />
+        {/* An unclaimed admin invite has provably never authenticated, so
+            last_seen_at is just the row-creation default (it equals
+            created_at). Render the truth — "Never" — rather than a
+            timestamp that reads like a real visit. */}
+        <TimeCell
+          value={pendingInvite ? null : u.last_seen_at}
+          emptyLabel={pendingInvite ? 'Never' : '—'}
+        />
       </tr>
       {state === 'pending' && u.beta_request_reason ? (
         <tr className="user-row-reason">
@@ -345,8 +352,8 @@ function UserRow({ user: u, busy, onChangeRole, onToggleMute, onFlipPermission }
 // Render a "YYYY-MM-DD HH:MM:SS" timestamp as an intentional date-over-time
 // stack (date prominent, time quiet below) rather than letting a narrow
 // column wrap the value mid-string. Falls back to an em-dash when absent.
-function TimeCell({ value }) {
-  if (!value) return <td className="muted">—</td>
+function TimeCell({ value, emptyLabel = '—' }) {
+  if (!value) return <td className="muted">{emptyLabel}</td>
   const [date, ...rest] = String(value).split(' ')
   const time = rest.join(' ')
   return (