feat: 来源归因规则引擎（渠道/AI/搜索词/诚实状态/历史重算）

- constants 规则库 v1：AI/引擎/社交域名表、搜索词参数白名单、付费点击参数、
  应用内 UA 标记、CHANNELS 枚举；page_view 白名单开 nav_type/prerendering
- services/attribution.classify 纯函数：付费>AI>引擎>社交>referral 分层，
  UTM 证据叠加（combined/conflict/label_only），应用内 UA 叠加/兜底，
  引擎 TLD 国家 variant，搜索词白名单提取（Google 恒空不虚构）
- SourceClassification 派生表（迁移 0004）：first_touch/session_entry 双 scope，
  rule_version 可追溯
- ingest 增量 best-effort：首访客/新会话时分类落库（savepoint+静默，
  失败不影响采集）；validation 对 page_view referrer 完整 URL 参数清洗+截500
- recompute_attribution 命令：全量/按站幂等重算
- API：访客列表归因五字段+channel 筛选、详情 attribution 块（含最近5会话入口）、
  dashboard channels 聚合（sources 原口径保留）；TS VisitorListParams 加 channel
- 测试 97 → 124（引擎20 + 集成/接口7）

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

server/tracker/tests/test_dashboard.py

@@ -3,7 +3,7 @@ from datetime import timedelta
 from django.contrib.auth import get_user_model
 from django.utils import timezone
 from rest_framework.test import APIClient
-from tracker.models import Event, Site, VisitSession, Visitor
+from tracker.models import Event, Site, SourceClassification, VisitSession, Visitor
 from tracker.services.stats import refresh_daily
 
 pytestmark = pytest.mark.django_db
@@ -104,6 +104,33 @@ def test_overview_trend_uses_dailystat_history(client, member_user):
     assert d["trend"][-1]["pv"] == 0   # 今天无事件，实时覆盖为 0
 
 
+def test_overview_channels_aggregation(client, member_user):
+    """channels：当天会话按 session_entry 分类的 channel 聚合（与 sources 并存，互不影响）。"""
+    _auth(client, member_user)
+    site = Site.objects.create(name="s", domains=["a.com"])
+    v1 = _visitor(site, "v1", last_seen=timezone.now())
+    v2 = _visitor(site, "v2", last_seen=timezone.now())
+    s1 = _session(site, v1, "s1", referrer="www.bing.com")
+    s2 = _session(site, v1, "s2", referrer="www.bing.com")
+    s3 = _session(site, v2, "s3", referrer="chatgpt.com")
+    s4 = _session(site, v2, "s4", referrer="")                      # 直接访问
+    SourceClassification.objects.create(site=site, visitor=v1, session=s1,
+        scope="session_entry", channel="natural_search", platform="Bing")
+    SourceClassification.objects.create(site=site, visitor=v1, session=s2,
+        scope="session_entry", channel="natural_search", platform="Bing")
+    SourceClassification.objects.create(site=site, visitor=v2, session=s3,
+        scope="session_entry", channel="ai_referral", platform="ChatGPT")
+    SourceClassification.objects.create(site=site, visitor=v2, session=s4,
+        scope="session_entry", channel="direct", resolution="unknown")
+    _events(site, v1, s1, 2, "/", prefix="a")
+
+    d = client.get("/api/admin/dashboard/overview").json()["data"]
+    assert d["channels"] == [{"channel": "natural_search", "sessions": 2},
+                             {"channel": "ai_referral", "sessions": 1},
+                             {"channel": "direct", "sessions": 1}]   # 倒序 top8，平局按名稳定
+    assert d["sources"][0] == {"source": "www.bing.com", "sessions": 2}  # 原口径保留
+
+
 def test_overview_site_filter_and_404(client, member_user):
     _auth(client, member_user)
     site_a = Site.objects.create(name="a", domains=["a.com"])