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/tests/test_station_model.py

@@ -0,0 +1,55 @@
+"""Test the Station and StationRecipeAssignment ORM models."""
+import pytest
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from models.station import Station, StationRecipeAssignment
+from tests.conftest import _create_user, create_test_recipe
+
+
+async def test_create_station(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="admin1", is_admin=True)
+    station = Station(
+        code="ST-001",
+        name="Linea 1",
+        location="Reparto Nord",
+        created_by=admin.id,
+    )
+    db_session.add(station)
+    await db_session.flush()
+    await db_session.refresh(station)
+    assert station.id is not None
+    assert station.active is True
+    assert station.created_at is not None
+
+
+async def test_station_code_is_unique(db_session: AsyncSession):
+    from sqlalchemy.exc import IntegrityError
+    admin = await _create_user(db_session, username="admin2", is_admin=True)
+    db_session.add(Station(code="ST-DUP", name="A", created_by=admin.id))
+    await db_session.flush()
+    db_session.add(Station(code="ST-DUP", name="B", created_by=admin.id))
+    with pytest.raises(IntegrityError):
+        await db_session.flush()
+    await db_session.rollback()
+
+
+async def test_assign_recipe_to_station(db_session: AsyncSession):
+    admin = await _create_user(db_session, username="admin3", is_admin=True)
+    station = Station(code="ST-002", name="Linea 2", created_by=admin.id)
+    db_session.add(station)
+    await db_session.flush()
+    recipe = await create_test_recipe(db_session, user_id=admin.id, code="REC-X")
+    assignment = StationRecipeAssignment(
+        station_id=station.id, recipe_id=recipe.id, assigned_by=admin.id,
+    )
+    db_session.add(assignment)
+    await db_session.flush()
+    result = await db_session.execute(
+        select(StationRecipeAssignment).where(
+            StationRecipeAssignment.station_id == station.id
+        )
+    )
+    assignments = result.scalars().all()
+    assert len(assignments) == 1
+    assert assignments[0].recipe_id == recipe.id