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/migrations/0004_sourceclassification.py

@@ -0,0 +1,37 @@
+# Generated by Django 5.2.17 on 2026-09-16 08:52
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('tracker', '0003_rawbatch'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='SourceClassification',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('scope', models.CharField(max_length=16)),
+                ('channel', models.CharField(blank=True, default='', max_length=32)),
+                ('platform', models.CharField(blank=True, default='', max_length=64)),
+                ('variant', models.CharField(blank=True, default='', max_length=64)),
+                ('search_term', models.CharField(blank=True, default='', max_length=200)),
+                ('evidence_kind', models.CharField(blank=True, default='', max_length=32)),
+                ('resolution', models.CharField(blank=True, default='', max_length=16)),
+                ('detail', models.JSONField(blank=True, default=dict)),
+                ('rule_version', models.CharField(default='v1', max_length=16)),
+                ('computed_at', models.DateTimeField(auto_now=True)),
+                ('session', models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, related_name='source_classifications', to='tracker.visitsession')),
+                ('site', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='source_classifications', to='tracker.site')),
+                ('visitor', models.ForeignKey(null=True, on_delete=django.db.models.deletion.CASCADE, related_name='source_classifications', to='tracker.visitor')),
+            ],
+            options={
+                'db_table': 'source_classification',
+                'indexes': [models.Index(fields=['site', 'visitor', 'scope'], name='source_clas_site_id_58ad9c_idx'), models.Index(fields=['site', 'channel'], name='source_clas_site_id_f08b23_idx')],
+            },
+        ),
+    ]