feat: implement user defaults persistence (Step 9.3)

Add user_defaults table and repository for persisting form defaults
across sessions. Feed and egg forms now load/save user preferences.

Changes:
- Add migration 0009-user-defaults.sql with table schema
- Add UserDefault model and UserDefaultsRepository
- Integrate defaults into feed route (location, feed_type, amount)
- Integrate defaults into egg route (location)
- Add repository unit tests and route integration tests

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/test_repositories_user_defaults.py

@@ -0,0 +1,158 @@
+# ABOUTME: Tests for UserDefaultsRepository.
+# ABOUTME: Validates CRUD operations for user form defaults.
+
+import time
+
+import pytest
+
+from animaltrack.models.reference import UserDefault
+from animaltrack.repositories.user_defaults import UserDefaultsRepository
+
+
+@pytest.fixture
+def now_utc():
+    """Current time in milliseconds since epoch."""
+    return int(time.time() * 1000)
+
+
+class TestUserDefaultsRepository:
+    """Tests for UserDefaultsRepository."""
+
+    def test_get_returns_none_for_missing(self, seeded_db):
+        """get returns None when no defaults exist."""
+        repo = UserDefaultsRepository(seeded_db)
+        result = repo.get("ppetru", "collect_egg")
+        assert result is None
+
+    def test_upsert_creates_new_record(self, seeded_db, now_utc):
+        """upsert creates a new defaults record."""
+        repo = UserDefaultsRepository(seeded_db)
+        defaults = UserDefault(
+            username="ppetru",
+            action="collect_egg",
+            location_id="01ARZ3NDEKTSV4RRFFQ69G5FAV",
+            updated_at_utc=now_utc,
+        )
+        repo.upsert(defaults)
+
+        result = repo.get("ppetru", "collect_egg")
+        assert result is not None
+        assert result.username == "ppetru"
+        assert result.action == "collect_egg"
+        assert result.location_id == "01ARZ3NDEKTSV4RRFFQ69G5FAV"
+
+    def test_upsert_updates_existing_record(self, seeded_db, now_utc):
+        """upsert updates an existing defaults record."""
+        repo = UserDefaultsRepository(seeded_db)
+        defaults = UserDefault(
+            username="ppetru",
+            action="feed_given",
+            location_id="01ARZ3NDEKTSV4RRFFQ69G5FAV",
+            feed_type_code="layer",
+            amount_kg=20,
+            updated_at_utc=now_utc,
+        )
+        repo.upsert(defaults)
+
+        updated = UserDefault(
+            username="ppetru",
+            action="feed_given",
+            location_id="01ARZ3NDEKTSV4RRFFQ69G5ABC",
+            feed_type_code="grower",
+            amount_kg=25,
+            updated_at_utc=now_utc + 1000,
+        )
+        repo.upsert(updated)
+
+        result = repo.get("ppetru", "feed_given")
+        assert result.location_id == "01ARZ3NDEKTSV4RRFFQ69G5ABC"
+        assert result.feed_type_code == "grower"
+        assert result.amount_kg == 25
+
+    def test_get_returns_all_fields(self, seeded_db, now_utc):
+        """get returns all stored fields correctly."""
+        repo = UserDefaultsRepository(seeded_db)
+        defaults = UserDefault(
+            username="ppetru",
+            action="feed_given",
+            location_id="01ARZ3NDEKTSV4RRFFQ69G5FAV",
+            species="duck",
+            animal_filter="location:strip1",
+            feed_type_code="layer",
+            amount_kg=20,
+            bag_size_kg=25,
+            updated_at_utc=now_utc,
+        )
+        repo.upsert(defaults)
+
+        result = repo.get("ppetru", "feed_given")
+        assert result.location_id == "01ARZ3NDEKTSV4RRFFQ69G5FAV"
+        assert result.species == "duck"
+        assert result.animal_filter == "location:strip1"
+        assert result.feed_type_code == "layer"
+        assert result.amount_kg == 20
+        assert result.bag_size_kg == 25
+
+    def test_different_actions_are_independent(self, seeded_db, now_utc):
+        """Different actions for same user are stored independently."""
+        repo = UserDefaultsRepository(seeded_db)
+        egg_defaults = UserDefault(
+            username="ppetru",
+            action="collect_egg",
+            location_id="01ARZ3NDEKTSV4RRFFQ69G5EGG",
+            updated_at_utc=now_utc,
+        )
+        feed_defaults = UserDefault(
+            username="ppetru",
+            action="feed_given",
+            location_id="01ARZ3NDEKTSV4RRFFQ69G5FED",
+            updated_at_utc=now_utc,
+        )
+        repo.upsert(egg_defaults)
+        repo.upsert(feed_defaults)
+
+        egg_result = repo.get("ppetru", "collect_egg")
+        feed_result = repo.get("ppetru", "feed_given")
+
+        assert egg_result.location_id == "01ARZ3NDEKTSV4RRFFQ69G5EGG"
+        assert feed_result.location_id == "01ARZ3NDEKTSV4RRFFQ69G5FED"
+
+    def test_different_users_are_independent(self, seeded_db, now_utc):
+        """Different users have independent defaults."""
+        repo = UserDefaultsRepository(seeded_db)
+        ppetru_defaults = UserDefault(
+            username="ppetru",
+            action="collect_egg",
+            location_id="01ARZ3NDEKTSV4RRFFQ69G5PPP",
+            updated_at_utc=now_utc,
+        )
+        ines_defaults = UserDefault(
+            username="ines",
+            action="collect_egg",
+            location_id="01ARZ3NDEKTSV4RRFFQ69G5III",
+            updated_at_utc=now_utc,
+        )
+        repo.upsert(ppetru_defaults)
+        repo.upsert(ines_defaults)
+
+        ppetru_result = repo.get("ppetru", "collect_egg")
+        ines_result = repo.get("ines", "collect_egg")
+
+        assert ppetru_result.location_id == "01ARZ3NDEKTSV4RRFFQ69G5PPP"
+        assert ines_result.location_id == "01ARZ3NDEKTSV4RRFFQ69G5III"
+
+    def test_null_fields_preserved(self, seeded_db, now_utc):
+        """Null fields are stored and retrieved correctly."""
+        repo = UserDefaultsRepository(seeded_db)
+        defaults = UserDefault(
+            username="ppetru",
+            action="collect_egg",
+            location_id=None,
+            species=None,
+            updated_at_utc=now_utc,
+        )
+        repo.upsert(defaults)
+
+        result = repo.get("ppetru", "collect_egg")
+        assert result.location_id is None
+        assert result.species is None