Show match demand in metrics (Refs #138)

src/routes/metrics/+page.svelte

@@ -255,7 +255,7 @@
         </div>
     {/if}
     <p class="range">{scopeLabel} · {format.period(report.since)} – {format.period(report.now)}</p>
-    {#if captured > 0}<MetricsSummary {report} />{/if}
+    <MetricsSummary {report} />
     {#if captured === 0}
         <Card>
             <EmptyState
@@ -312,6 +312,8 @@
             disabled={scopeNavigating}
             onTimeZoneChange={(value) => changeScope({ timeZone: value })}
         />
+    {/if}
+    {#if captured > 0 || report.matches.started > 0}
         <Tabs
             tabs={[
                 { id: 'maps', label: 'Maps' },
@@ -379,6 +381,16 @@
             including unknown status. Empty spares are expected when an autoscaling policy keeps
             lobbies ready.
         </p>
+        <p>
+            Matches started counts retained matches whose start time falls within this report’s
+            window, including both endpoints and all match statuses. If a match did not report a
+            start time, its first observation is used. Average group is the mean number of distinct
+            recorded players across each match’s lifetime, including later arrivals. Solo means
+            exactly one recorded player. Both average group and solo share exclude matches with no
+            recorded players; those matches still count as started. Ongoing matches can change as
+            players join. Match records are independent of sampled lobby occupancy, and missing or
+            purged records are not estimated.
+        </p>
         <p>
             No empty lobby measures map time when at least one lobby has known occupancy and no
             tracked lobby reports zero players. If every lobby is unknown, map availability is
@@ -389,8 +401,9 @@
         </p>
         <p>
             Each periodic observation covers at most {ONLINE_MAX_MS / 1000} seconds. Longer collection
-            gaps are excluded. History is retained for 31 days. Player-hours include all players reported
-            by the server and are estimates, not individual session records.
+            gaps are excluded. Occupancy history defaults to 31 days; saved match retention is configured
+            separately. Player-hours include all players reported by the server and are estimates, not
+            individual session records.
         </p>
         <p>
             Timeline buckets are aligned to UTC, with labels shown in {report.scope.timeZone.replaceAll(