chore: dashboard 确定性排序与注释修正

- sources/top_pages Top8 加平局次序键（referrer_domain/path），
  平局时跨请求顺序稳定
- test_dashboard 修正过时注释（b 站数据同为 refresh_daily 真实落行）

pytest 79 passed 无回归。

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

server/tracker/api/dashboard.py

@@ -72,7 +72,8 @@ class OverviewView(EnvelopeMixin, APIView):
             q = q.filter(site=site)
         return [{"source": r["referrer_domain"] or "直接访问", "sessions": r["n"]}
                 for r in q.values("referrer_domain")
-                         .annotate(n=Count("id")).order_by("-n")[:8]]
+                         .annotate(n=Count("id"))
+                         .order_by("-n", "referrer_domain")[:8]]   # 平局时次序跨请求稳定
 
     def _today_pages(self, site, today):
         start, end = _day_bounds(today)
@@ -82,4 +83,5 @@ class OverviewView(EnvelopeMixin, APIView):
             q = q.filter(site=site)
         return [{"path": r["path"], "pv": r["n"]}
                 for r in q.values("path")
-                         .annotate(n=Count("id")).order_by("-n")[:8]]
+                         .annotate(n=Count("id"))
+                         .order_by("-n", "path")[:8]]   # 平局时次序跨请求稳定

server/tracker/tests/test_dashboard.py

@@ -92,7 +92,7 @@ def test_overview_trend_uses_dailystat_history(client, member_user):
     sa = _session(site_a, va, "sa", at=yn)
     _events(site_a, va, sa, 3, "/", at=yn, prefix="ya")
     refresh_daily(site_a, YESTERDAY)
-    # b 站昨天直接落一行（site=None 时验证 Sum 跨站点聚合）
+    # b 站昨天 4 事件同样走 refresh_daily——两站各落一行，验证 site=None 的跨站 Sum
     vb = Visitor.objects.create(site=site_b, visitor_id="vb")
     sb = _session(site_b, vb, "sb", at=yn)
     _events(site_b, vb, sb, 4, "/", at=yn, prefix="yb")