feat: merge cartsnitch/api into api/ subdirectory

Consolidate API gateway service into monorepo.
Squashed from https://github.com/cartsnitch/api main (89bacb1).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/cartsnitch_api/models/shrinkflation.py

@@ -0,0 +1,41 @@
+"""ShrinkflationEvent model."""
+
+import uuid
+from datetime import date
+from decimal import Decimal
+from typing import TYPE_CHECKING
+
+from sqlalchemy import Date, ForeignKey, Numeric, String
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from cartsnitch_api.constants import SizeUnit
+from cartsnitch_api.models.base import Base, TimestampMixin, UUIDPrimaryKeyMixin
+
+if TYPE_CHECKING:
+    from cartsnitch_api.models.product import NormalizedProduct
+
+
+class ShrinkflationEvent(UUIDPrimaryKeyMixin, TimestampMixin, Base):
+    """Detected shrinkflation event — product size changed while price held or rose."""
+
+    __tablename__ = "shrinkflation_events"
+
+    normalized_product_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("normalized_products.id"), nullable=False
+    )
+    detected_date: Mapped[date] = mapped_column(Date, nullable=False)
+    old_size: Mapped[str] = mapped_column(String(50), nullable=False)
+    new_size: Mapped[str] = mapped_column(String(50), nullable=False)
+    old_unit: Mapped[SizeUnit] = mapped_column(String(10), nullable=False)
+    new_unit: Mapped[SizeUnit] = mapped_column(String(10), nullable=False)
+    price_at_old_size: Mapped[Decimal | None] = mapped_column(Numeric(10, 2))
+    price_at_new_size: Mapped[Decimal | None] = mapped_column(Numeric(10, 2))
+    confidence: Mapped[Decimal] = mapped_column(
+        Numeric(3, 2), nullable=False, default=Decimal("1.00")
+    )
+    notes: Mapped[str | None] = mapped_column(String(1000))
+
+    # Relationships
+    normalized_product: Mapped["NormalizedProduct"] = relationship(
+        back_populates="shrinkflation_events"
+    )