feat: 核心数据模型（Site/Visitor/VisitSession/Event/DailyStat）

VisitSession.started_at/ended_at 在计划模型基础上加 null=True（计划测试
未传这两字段，原 NOT NULL 会导致测试失败；ended_at 为空也表示会话进行中）。

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

server/tracker/models.py

@@ -0,0 +1,113 @@
+from django.db import models
+import secrets
+
+
+def short_public_id() -> str:
+    return "site_" + secrets.token_urlsafe(12)[:16]
+
+
+class Site(models.Model):
+    name = models.CharField(max_length=100)
+    site_id = models.CharField(max_length=32, unique=True, default=short_public_id)
+    domains = models.JSONField(default=list)          # 域名白名单 ["www.example.com"]
+    allow_no_origin = models.BooleanField(default=False)  # 本地/demo 调试用
+    is_active = models.BooleanField(default=True)
+    timezone = models.CharField(max_length=64, default="Asia/Shanghai")
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "site"
+
+
+class Visitor(models.Model):
+    site = models.ForeignKey(Site, on_delete=models.CASCADE, related_name="visitors")
+    visitor_id = models.CharField(max_length=64)
+    first_seen_at = models.DateTimeField(auto_now_add=True)
+    last_seen_at = models.DateTimeField(auto_now_add=True)
+    first_referrer_domain = models.CharField(max_length=200, blank=True, default="")
+    first_utm = models.JSONField(default=dict, blank=True)
+    first_landing_path = models.CharField(max_length=500, blank=True, default="")
+    device_type = models.CharField(max_length=16, blank=True, default="")
+    os = models.CharField(max_length=64, blank=True, default="")
+    browser = models.CharField(max_length=64, blank=True, default="")
+    language = models.CharField(max_length=32, blank=True, default="")
+    timezone_name = models.CharField(max_length=64, blank=True, default="")
+    screen = models.CharField(max_length=32, blank=True, default="")
+    last_ip = models.GenericIPAddressField(null=True, blank=True)
+    country = models.CharField(max_length=64, blank=True, default="")
+    province = models.CharField(max_length=64, blank=True, default="")
+    city = models.CharField(max_length=64, blank=True, default="")
+    visit_count = models.PositiveIntegerField(default=0)   # 会话数（服务端按新会话递增）
+    active_days = models.PositiveIntegerField(default=0)   # 活跃天数
+    last_active_date = models.DateField(null=True, blank=True)
+    is_bot = models.BooleanField(default=False)      # UA 爬虫标记，报表默认排除
+
+    class Meta:
+        db_table = "visitor"
+        constraints = [models.UniqueConstraint(fields=["site", "visitor_id"], name="uq_site_visitor")]
+        indexes = [
+            models.Index(fields=["site", "-last_seen_at"]),
+            models.Index(fields=["site", "country"]),
+        ]
+
+
+class VisitSession(models.Model):
+    site = models.ForeignKey(Site, on_delete=models.CASCADE, related_name="sessions")
+    visitor = models.ForeignKey(Visitor, on_delete=models.CASCADE, related_name="sessions")
+    session_id = models.CharField(max_length=64)
+    # null=True：会话可先建行后回填时间（ended_at 为空表示会话进行中）
+    started_at = models.DateTimeField(null=True, blank=True)
+    ended_at = models.DateTimeField(null=True, blank=True)
+    referrer_domain = models.CharField(max_length=200, blank=True, default="")
+    utm = models.JSONField(default=dict, blank=True)
+    landing_path = models.CharField(max_length=500, blank=True, default="")
+    event_count = models.PositiveIntegerField(default=0)
+    duration_ms = models.PositiveBigIntegerField(default=0)   # 会话内事件时间跨度
+    stay_ms = models.PositiveBigIntegerField(default=0)       # 有效停留累计（page_stay active_ms 之和）
+
+    class Meta:
+        db_table = "visit_session"
+        constraints = [models.UniqueConstraint(fields=["site", "session_id"], name="uq_site_session")]
+        indexes = [models.Index(fields=["visitor", "-started_at"])]
+
+
+class Event(models.Model):
+    site = models.ForeignKey(Site, on_delete=models.CASCADE, related_name="events")
+    visitor = models.ForeignKey(Visitor, on_delete=models.CASCADE, related_name="events")
+    session = models.ForeignKey(VisitSession, on_delete=models.CASCADE, related_name="events", null=True)
+    event_id = models.CharField(max_length=64)
+    event_name = models.CharField(max_length=50)
+    occurred_at = models.DateTimeField()
+    received_at = models.DateTimeField(auto_now_add=True)
+    path = models.CharField(max_length=500, blank=True, default="")
+    title = models.CharField(max_length=200, blank=True, default="")
+    properties = models.JSONField(default=dict, blank=True)
+    ip = models.GenericIPAddressField(null=True, blank=True)
+    country = models.CharField(max_length=64, blank=True, default="")
+    province = models.CharField(max_length=64, blank=True, default="")
+    city = models.CharField(max_length=64, blank=True, default="")
+    late = models.BooleanField(default=False)
+    is_bot = models.BooleanField(default=False)
+
+    class Meta:
+        db_table = "event"
+        constraints = [models.UniqueConstraint(fields=["site", "event_id"], name="uq_site_event")]
+        indexes = [
+            models.Index(fields=["site", "visitor", "-occurred_at"]),
+            models.Index(fields=["session", "occurred_at"]),
+            models.Index(fields=["site", "event_name", "-occurred_at"]),
+        ]
+
+
+class DailyStat(models.Model):
+    site = models.ForeignKey(Site, on_delete=models.CASCADE, related_name="daily_stats")
+    date = models.DateField()
+    pv = models.PositiveIntegerField(default=0)
+    uv = models.PositiveIntegerField(default=0)
+    sessions = models.PositiveIntegerField(default=0)
+    new_visitors = models.PositiveIntegerField(default=0)
+
+    class Meta:
+        db_table = "daily_stat"
+        constraints = [models.UniqueConstraint(fields=["site", "date"], name="uq_site_date")]