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/price.py

@@ -0,0 +1,50 @@
+"""PriceHistory model — tracks product prices over time."""
+
+import uuid
+from datetime import date
+from decimal import Decimal
+from typing import TYPE_CHECKING
+
+from sqlalchemy import Date, ForeignKey, Index, Numeric, String
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from cartsnitch_api.constants import PriceSource
+from cartsnitch_api.models.base import Base, TimestampMixin, UUIDPrimaryKeyMixin
+
+if TYPE_CHECKING:
+    from cartsnitch_api.models.product import NormalizedProduct
+    from cartsnitch_api.models.purchase import PurchaseItem
+    from cartsnitch_api.models.store import Store
+
+
+class PriceHistory(UUIDPrimaryKeyMixin, TimestampMixin, Base):
+    """A single price observation for a product at a store on a date."""
+
+    __tablename__ = "price_history"
+    __table_args__ = (
+        Index(
+            "ix_price_history_product_store_date",
+            "normalized_product_id",
+            "store_id",
+            "observed_date",
+        ),
+    )
+
+    normalized_product_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("normalized_products.id"), nullable=False
+    )
+    store_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("stores.id"), nullable=False)
+    observed_date: Mapped[date] = mapped_column(Date, nullable=False)
+    regular_price: Mapped[Decimal] = mapped_column(Numeric(10, 2), nullable=False)
+    sale_price: Mapped[Decimal | None] = mapped_column(Numeric(10, 2))
+    loyalty_price: Mapped[Decimal | None] = mapped_column(Numeric(10, 2))
+    coupon_price: Mapped[Decimal | None] = mapped_column(Numeric(10, 2))
+    source: Mapped[PriceSource] = mapped_column(String(20), nullable=False)
+    purchase_item_id: Mapped[uuid.UUID | None] = mapped_column(ForeignKey("purchase_items.id"))
+
+    # Relationships
+    normalized_product: Mapped["NormalizedProduct"] = relationship(back_populates="price_histories")
+    store: Mapped["Store"] = relationship(back_populates="price_histories")
+    purchase_item: Mapped["PurchaseItem | None"] = relationship(
+        back_populates="price_history_entries"
+    )