Add email sending toggle and fix event timestamp default

Introduces enable_email_sending to control real email delivery in config. Updates Event.created_at to use default_factory for correct timestamp initialization.

app/config.py

@@ -119,6 +119,7 @@ class Settings(BaseSettings):
 
     # 邮件服务设置
     enable_email_verification: bool = Field(default=False, description="是否启用邮件验证功能")
+    enable_email_sending: bool = Field(default=False, description="是否真实发送邮件（false时仅模拟发送，输出到日志）")
     smtp_server: str = "localhost"
     smtp_port: int = 587
     smtp_username: str = ""

app/database/events.py

@@ -41,7 +41,7 @@ class EventType(str, Enum):
 class Event(UTCBaseModel, SQLModel, table=True):
     __tablename__: str = "user_events"
     id: int = Field(default=None, primary_key=True)
-    created_at: datetime = Field(sa_column=Column(DateTime(timezone=True), default_factory=utcnow))
+    created_at: datetime = Field(default_factory=utcnow, sa_column=Column(DateTime(timezone=True), default=utcnow))
     type: EventType
     event_payload: dict = Field(exclude=True, default_factory=dict, sa_column=Column(JSON))
     user_id: int | None = Field(