fix: new_visitors 排爬虫+日界/爬虫口径回归测试

- refresh_daily new_visitors 加 is_bot=False（爬虫不是受众，四指标口径统一）
- test_refresh_daily_shanghai_boundary：固定 UTC 时间戳钉死上海自然日界
- test_refresh_daily_excludes_bots：事件/会话/访客 is_bot 均不计入
- refresh_stats 删未使用的 stat = 赋值

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

server/tracker/tests/test_stats.py

@@ -1,4 +1,4 @@
-from datetime import timedelta
+from datetime import date, timedelta
 from django.utils import timezone
 from tracker.models import Site, Visitor, VisitSession, Event
 from tracker.services.stats import refresh_daily
@@ -28,3 +28,33 @@ def test_refresh_daily_two_days(db):
     # （auto_now_add），故昨天 new=0、今天 new=2（v1+v2）——按 first_seen_at 真实语义断言
     assert (y.pv, y.uv, y.sessions, y.new_visitors) == (3, 1, 1, 0)
     assert (t.pv, t.uv, t.sessions, t.new_visitors) == (6, 2, 2, 2)   # 今天：pv=6 uv=2(v1+v2) sessions=2 new=2(v1+v2)
+
+def test_refresh_daily_shanghai_boundary(db):
+    # 固定时间戳钉死日界（不依赖运行时刻）：UTC 2026-09-15T16:30 = 上海 09-16 00:30 → 落 9-16 不落 9-15
+    site = Site.objects.create(name="s", domains=["a.com"])
+    v = Visitor.objects.create(site=site, visitor_id="v")
+    s = VisitSession.objects.create(site=site, visitor=v, session_id="s",
+        started_at="2026-09-15T16:30:00Z", ended_at="2026-09-15T16:30:00Z")
+    Event.objects.create(site=site, visitor=v, session=s, event_id="e",
+        event_name="page_view", occurred_at="2026-09-15T16:30:00Z", path="/")
+    d15 = refresh_daily(site, date(2026, 9, 15))
+    d16 = refresh_daily(site, date(2026, 9, 16))
+    assert (d15.pv, d16.pv) == (0, 1)
+
+def test_refresh_daily_excludes_bots(db):
+    # 爬虫口径：事件/会话/访客三处 is_bot 均不计入四指标（与 pv/uv/sessions 统一）
+    site = Site.objects.create(name="s", domains=["a.com"])
+    bot = Visitor.objects.create(site=site, visitor_id="bot", is_bot=True)
+    human = Visitor.objects.create(site=site, visitor_id="human")
+    bs = VisitSession.objects.create(site=site, visitor=bot, session_id="bs",
+        started_at="2026-09-15T10:00:00Z", ended_at="2026-09-15T10:01:00Z")
+    hs = VisitSession.objects.create(site=site, visitor=human, session_id="hs",
+        started_at="2026-09-15T10:00:00Z", ended_at="2026-09-15T10:01:00Z")
+    Event.objects.create(site=site, visitor=bot, session=bs, event_id="b1",
+        event_name="page_view", occurred_at="2026-09-15T10:00:00Z", path="/", is_bot=True)
+    Event.objects.create(site=site, visitor=human, session=hs, event_id="h1",
+        event_name="page_view", occurred_at="2026-09-15T10:00:30Z", path="/")
+    d = refresh_daily(site, date(2026, 9, 15))
+    assert (d.pv, d.uv, d.sessions) == (1, 1, 1)   # 只计 human 的事件/会话
+    t = refresh_daily(site, timezone.localdate())  # 两位访客 first_seen_at 均为运行时，刷今天窗口才能非空验证 new_visitors
+    assert t.new_visitors == 1                     # 爬虫访客不计入新增