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/product.py

@@ -0,0 +1,39 @@
+"""NormalizedProduct model — the canonical product identity."""
+
+from typing import TYPE_CHECKING
+
+from sqlalchemy import JSON, String
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from cartsnitch_api.constants import ProductCategory, SizeUnit
+from cartsnitch_api.models.base import Base, TimestampMixin, UUIDPrimaryKeyMixin
+
+if TYPE_CHECKING:
+    from cartsnitch_api.models.coupon import Coupon
+    from cartsnitch_api.models.price import PriceHistory
+    from cartsnitch_api.models.purchase import PurchaseItem
+    from cartsnitch_api.models.shrinkflation import ShrinkflationEvent
+
+
+class NormalizedProduct(UUIDPrimaryKeyMixin, TimestampMixin, Base):
+    """Canonical product identity — matches products across retailers."""
+
+    __tablename__ = "normalized_products"
+
+    canonical_name: Mapped[str] = mapped_column(String(300), nullable=False)
+    category: Mapped[ProductCategory | None] = mapped_column(String(50))
+    subcategory: Mapped[str | None] = mapped_column(String(100))
+    brand: Mapped[str | None] = mapped_column(String(200))
+    size: Mapped[str | None] = mapped_column(String(50))
+    size_unit: Mapped[SizeUnit | None] = mapped_column(String(10))
+    upc_variants: Mapped[list[str] | None] = mapped_column(JSON, default=list)
+
+    # Relationships
+    purchase_items: Mapped[list["PurchaseItem"]] = relationship(back_populates="normalized_product")
+    price_histories: Mapped[list["PriceHistory"]] = relationship(
+        back_populates="normalized_product"
+    )
+    coupons: Mapped[list["Coupon"]] = relationship(back_populates="normalized_product")
+    shrinkflation_events: Mapped[list["ShrinkflationEvent"]] = relationship(
+        back_populates="normalized_product"
+    )