Add models for EmailTemplate, ActivityLog, and NotificationLog

Introduced new database models to handle email templates, activity logs, and notification logs, including relevant enums and utilities. Updated ER diagram to reflect new relationships and attributes, enhancing event tracking and notification management capabilities.

backend/app/models/notification_log.py

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+from datetime import datetime, timezone
+from enum import Enum
+
+from sqlalchemy import Column, String, ForeignKey, Enum as SQLEnum, Text, DateTime
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from sqlalchemy.orm import relationship
+
+from .base import Base, TimestampMixin, UUIDMixin
+
+
+class NotificationType(str, Enum):
+    EMAIL = "email"
+    SMS = "sms"
+    PUSH = "push"
+    IN_APP = "in_app"
+
+
+class NotificationStatus(str, Enum):
+    QUEUED = "queued"
+    SENT = "sent"
+    DELIVERED = "delivered"
+    FAILED = "failed"
+    OPENED = "opened"
+    CLICKED = "clicked"
+
+
+class NotificationLog(Base, UUIDMixin, TimestampMixin):
+    __tablename__ = 'notification_logs'
+
+    # Notification Details
+    notification_type = Column(SQLEnum(NotificationType), nullable=False)
+    status = Column(SQLEnum(NotificationStatus), nullable=False, default=NotificationStatus.QUEUED)
+
+    # Content
+    subject = Column(String)
+    content_preview = Column(String(255))  # Short preview of content
+    template_id = Column(UUID(as_uuid=True), ForeignKey('email_templates.id'))
+
+    # Recipient Information
+    event_id = Column(UUID(as_uuid=True), ForeignKey('events.id'), nullable=False)
+    guest_id = Column(UUID(as_uuid=True), ForeignKey('guests.id'))  # Optional, if sent to a specific guest
+    recipient = Column(String, nullable=False)  # Email address or phone number
+
+    # Tracking
+    sent_at = Column(DateTime(timezone=True))
+    delivered_at = Column(DateTime(timezone=True))
+    opened_at = Column(DateTime(timezone=True))
+    error_message = Column(Text)
+    retry_count = Column(Integer, default=0)
+    external_id = Column(String)  # ID from external provider (SendGrid, Twilio, etc.)
+
+    # Additional Data
+    metadata = Column(JSONB, default=dict)
+
+    # Relationships
+    event = relationship("Event")
+    guest = relationship("Guest")
+    template = relationship("EmailTemplate")
+
+    def __repr__(self):
+        return f"<NotificationLog {self.notification_type.value} to {self.recipient} status={self.status.value}>"
+
+    def mark_sent(self):
+        """Mark notification as sent"""
+        self.status = NotificationStatus.SENT
+        self.sent_at = datetime.now(timezone.utc)
+
+    def mark_delivered(self):
+        """Mark notification as delivered"""
+        self.status = NotificationStatus.DELIVERED
+        self.delivered_at = datetime.now(timezone.utc)
+
+    def mark_opened(self):
+        """Mark notification as opened"""
+        self.status = NotificationStatus.OPENED
+        self.opened_at = datetime.now(timezone.utc)
+
+    def mark_failed(self, error: str):
+        """Mark notification as failed with error message"""
+        self.status = NotificationStatus.FAILED
+        self.error_message = error
+        self.retry_count += 1
+
+    @property
+    def can_retry(self):
+        """Check if notification can be retried (fewer than 3 attempts)"""
+        return self.status == NotificationStatus.FAILED and self.retry_count < 3