fix: show membership date for stores without pickups

Treat Foodsharing's zero lastFetch value as no pickup, store memberSince, and
show compact, visible mobile status information without hover tooltips.

src/components/MobileConfigList.js

@@ -9,14 +9,28 @@ const FILTER_OPTIONS = [
   { value: 'inactive', label: 'Inaktiv' }
 ];
 
-const formatLastPickup = (value) => {
-  const date = new Date(value);
-  if (!value || Number.isNaN(date.getTime())) {
-    return { relative: 'Unbekannt', exact: null };
+const formatDate = (date) => date.toLocaleDateString('de-DE', {
+  day: '2-digit',
+  month: '2-digit',
+  year: 'numeric'
+});
+
+const formatLastPickup = (lastPickupAt, memberSinceAt) => {
+  const date = new Date(lastPickupAt);
+  if (!lastPickupAt || Number.isNaN(date.getTime()) || date.getTime() <= 0) {
+    const memberSince = new Date(memberSinceAt);
+    return {
+      state: 'never',
+      memberSince: memberSinceAt && !Number.isNaN(memberSince.getTime())
+        ? formatDate(memberSince)
+        : null
+    };
   }
+  const ageDays = (Date.now() - date.getTime()) / (1000 * 60 * 60 * 24);
   return {
+    state: ageDays >= 90 ? 'stale' : 'current',
     relative: formatDistanceToNowStrict(date, { addSuffix: true, locale: de }),
-    exact: date.toLocaleDateString('de-DE')
+    exact: formatDate(date)
   };
 };
 
@@ -97,7 +111,7 @@ const MobileConfigList = ({
         {filteredEntries.map((entry) => {
           const range = entry.desiredDateRange || (entry.desiredDate ? { start: entry.desiredDate, end: entry.desiredDate } : null);
           const slots = formatRegularPickup(regularPickupMap?.[entry.id]);
-          const lastPickup = formatLastPickup(entry.lastPickupAt);
+          const lastPickup = formatLastPickup(entry.lastPickupAt, entry.memberSinceAt);
           return (
             <article
               key={entry.id}
@@ -109,8 +123,16 @@ const MobileConfigList = ({
                   <h3 className="mobile-config-card__title">{entry.label || `Store ${entry.id}`}</h3>
                   <p className="mobile-config-card__id">#{entry.id}</p>
                   {slots && <p className="mobile-config-card__slots">Slots: {slots}</p>}
-                  <p className="mobile-config-card__last-pickup" title={lastPickup.exact || undefined}>
-                    Letzte Abholung: <strong>{lastPickup.relative}</strong>
+                  <p className={`mobile-config-card__last-pickup mobile-config-card__last-pickup--${lastPickup.state}`}>
+                    {lastPickup.state === 'never' ? (
+                      <>
+                        Noch nicht abgeholt{lastPickup.memberSince && <> · Beitritt: <strong>{lastPickup.memberSince}</strong></>}
+                      </>
+                    ) : (
+                      <>
+                        Letzte Abholung: <strong>{lastPickup.relative}</strong> · {lastPickup.exact}
+                      </>
+                    )}
                   </p>
                 </div>
                 <a