fix(billing): show user balance and correct all-records summary scope

When the usage overview has no date filter, show only all-time totals instead
of a misleading 30-day range block; surface current balance in user analysis.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/admin/pages/BillingPage.tsx

@@ -432,11 +432,9 @@ function UsageOverviewPanel() {
     setLoadingSummary(true);
     setError(null);
     try {
-      const chartRange = start && end
-        ? { startDate: start, endDate: end }
-        : presetDateRange(30);
-      const { startAt, endAt } = dateRangeToUnix(chartRange.startDate, chartRange.endDate);
-      const data = await getAdminUsageSummary({ startAt, endAt });
+      const data = start && end
+        ? await getAdminUsageSummary(dateRangeToUnix(start, end))
+        : await getAdminUsageSummary();
       setSummary(data);
     } catch (err) {
       setError(err instanceof Error ? err.message : '汇总加载失败');
@@ -476,7 +474,7 @@ function UsageOverviewPanel() {
 
   const rangeSummaryLabel = hasDateFilter
     ? `区间汇总（${startDate} 至 ${endDate}）`
-    : '区间汇总（近 30 天）';
+    : '';
 
   return (
     <>
@@ -690,6 +688,16 @@ function UsageQueryPanel() {
         <p className="muted billing-empty">请选择用户，将自动加载用量与趋势图</p>
       )}
       {userId && loading && !result && !stats && <p className="muted">加载中…</p>}
+      {userId && selectedUser && (
+        <div className="usage-user-balance-bar">
+          <span className="usage-user-balance-name">
+            {selectedUser.displayName}
+            <span className="muted"> @{selectedUser.username}</span>
+          </span>
+          <span className="usage-user-balance-label muted">当前余额</span>
+          <span className="usage-user-balance-value">¥{formatYuan(selectedUser.balanceCents)}</span>
+        </div>
+      )}
       {userId && (
         <UsageSummaryPanel
           summary={summary}