feat: countdown anniversaries and birthdays like ticktick

backend/models.py

@@ -126,6 +126,24 @@ class RecurrenceException(Base):
     deleted: Mapped[bool] = mapped_column(Boolean, default=False)
 
 
+class Countdown(Base):
+    __tablename__ = "countdowns"
+    __table_args__ = (
+        Index("ix_countdowns_user_archive_date", "user_id", "archived_at", "event_date"),
+    )
+    id: Mapped[UUID] = mapped_column(primary_key=True, default=new_id)
+    user_id: Mapped[UUID] = mapped_column(ForeignKey("users.id", ondelete="CASCADE"), index=True)
+    title: Mapped[str] = mapped_column(String(200))
+    event_date: Mapped[date] = mapped_column(Date)
+    kind: Mapped[str] = mapped_column(String(16), default="countdown")
+    repeat_rule: Mapped[str] = mapped_column(String(16), default="none")
+    icon: Mapped[str] = mapped_column(String(32), default="📅")
+    pinned: Mapped[bool] = mapped_column(Boolean, default=False)
+    archived_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=utcnow)
+    updated_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=utcnow, onupdate=utcnow)
+
+
 class Habit(Base):
     __tablename__ = "habits"
     id: Mapped[UUID] = mapped_column(primary_key=True, default=new_id)