Show a paid club's cover end date in the health table

For a club on a plan whose dues are settled, the Dues cell now reads "until
<date> · paid" — the end of the current paid period, which is the day the grace
period would start if nothing renews. It is exactly the "when does this lapse?"
question the paid badge alone could not answer.

Driven by a new paid_until annotation: the furthest-out PAID period end, null when
the club owes or was never billed (so a fully-paid free tier shows just "paid",
and an owing club shows the amount, unchanged). It rides the SAME single query —
the assertNumQueries(1) test still holds — and the date is whitespace-nowrap so it
does not wrap in the narrow cell.

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

controlpanel/templates/controlpanel/_club_health_table.html

@@ -87,6 +87,10 @@
                         <div class="flex flex-row gap-2 items-center justify-end">
                             {% if not club.dues_owed %}
                                 {% if club.tier_name %}
+                                    {% comment %} paid_until is the current period's end — the day grace would start if nothing renews. {% endcomment %}
+                                    {% if club.paid_until %}
+                                        <span class="whitespace-nowrap text-xs opacity-60">until {{ club.paid_until|date:"j M Y" }}</span>
+                                    {% endif %}
                                     <span class="badge badge-success">paid</span>
                                 {% else %}
                                     <span class="badge badge-ghost badge-outline">n/a</span>