feat(models): add Station and StationRecipeAssignment models

TDD: test written first, confirmed failing with ModuleNotFoundError,
then model implemented; all 3 new tests pass. conftest updated to
import new models so Base.metadata.create_all picks up the tables.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/models/station.py

@@ -0,0 +1,69 @@
+"""Station and StationRecipeAssignment models.
+
+A Station represents a physical control point (typically one per tablet/PC).
+Recipes are assigned to stations so that each station only sees the products
+it is supposed to inspect.
+"""
+from datetime import datetime
+from typing import TYPE_CHECKING, Optional
+
+from sqlalchemy import Boolean, DateTime, ForeignKey, Integer, String, Text, UniqueConstraint, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from database import Base
+
+if TYPE_CHECKING:
+    from models.recipe import Recipe
+
+
+class Station(Base):
+    __tablename__ = "stations"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    code: Mapped[str] = mapped_column(String(100), unique=True, nullable=False, index=True)
+    name: Mapped[str] = mapped_column(String(255), nullable=False)
+    location: Mapped[Optional[str]] = mapped_column(String(255), nullable=True)
+    notes: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
+    active: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True, index=True)
+    created_by: Mapped[int] = mapped_column(Integer, ForeignKey("users.id"), nullable=False)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime, nullable=False, server_default=func.now()
+    )
+
+    assignments: Mapped[list["StationRecipeAssignment"]] = relationship(
+        back_populates="station", cascade="all, delete-orphan", lazy="selectin"
+    )
+
+    __table_args__ = (
+        {"mysql_engine": "InnoDB", "mysql_charset": "utf8mb4"},
+    )
+
+    def __repr__(self) -> str:
+        return f"<Station {self.code} '{self.name}'>"
+
+
+class StationRecipeAssignment(Base):
+    __tablename__ = "station_recipe_assignments"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    station_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("stations.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    recipe_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("recipes.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    assigned_by: Mapped[int] = mapped_column(Integer, ForeignKey("users.id"), nullable=False)
+    assigned_at: Mapped[datetime] = mapped_column(
+        DateTime, nullable=False, server_default=func.now()
+    )
+
+    station: Mapped["Station"] = relationship(back_populates="assignments")
+    recipe: Mapped["Recipe"] = relationship(lazy="selectin")
+
+    __table_args__ = (
+        UniqueConstraint("station_id", "recipe_id", name="uq_station_recipe"),
+        {"mysql_engine": "InnoDB", "mysql_charset": "utf8mb4"},
+    )
+
+    def __repr__(self) -> str:
+        return f"<StationRecipeAssignment station={self.station_id} recipe={self.recipe_id}>"