Add comprehensive automated testing infrastructure

Backend:
  - pytest configuration with async support and coverage
  - Unit tests for notification service (23 tests)
  - Unit tests for smart plug manager (12 tests)
  - Unit tests for archive service (16 tests)
  - Integration tests for API endpoints
  - Fix: notifications now send immediately (digest is summary only)

  Frontend:
  - Vitest configuration with jsdom and coverage
  - MSW for API mocking
  - Component tests for Toggle, Button, Card, ConfirmModal (77 tests)
  - Test utilities with custom render wrapper

  CI/CD:
  - GitHub Actions workflow for automated testing
  - Backend lint, unit tests, integration tests
  - Frontend lint, type-check, unit tests, build

backend/tests/integration/test_filaments_api.py

@@ -0,0 +1,117 @@
+"""Integration tests for Filaments API endpoints."""
+
+import pytest
+from httpx import AsyncClient
+
+
+class TestFilamentsAPI:
+    """Integration tests for /api/v1/filaments/ endpoints."""
+
+    @pytest.fixture
+    async def filament_factory(self, db_session):
+        """Factory to create test filaments."""
+        async def _create_filament(**kwargs):
+            from backend.app.models.filament import Filament
+
+            defaults = {
+                "name": "Test PLA",
+                "type": "PLA",
+                "color": "Red",
+                "color_hex": "#FF0000",
+                "brand": "Generic",
+                "cost_per_kg": 25.0,
+            }
+            defaults.update(kwargs)
+
+            filament = Filament(**defaults)
+            db_session.add(filament)
+            await db_session.commit()
+            await db_session.refresh(filament)
+            return filament
+
+        return _create_filament
+
+    @pytest.mark.asyncio
+    @pytest.mark.integration
+    async def test_list_filaments_empty(self, async_client: AsyncClient):
+        """Verify empty list when no filaments exist."""
+        response = await async_client.get("/api/v1/filaments/")
+        assert response.status_code == 200
+        assert isinstance(response.json(), list)
+
+    @pytest.mark.asyncio
+    @pytest.mark.integration
+    async def test_list_filaments_with_data(
+        self, async_client: AsyncClient, filament_factory, db_session
+    ):
+        """Verify list returns existing filaments."""
+        await filament_factory(name="Test Filament")
+        response = await async_client.get("/api/v1/filaments/")
+        assert response.status_code == 200
+        data = response.json()
+        assert any(f["name"] == "Test Filament" for f in data)
+
+    @pytest.mark.asyncio
+    @pytest.mark.integration
+    async def test_create_filament(self, async_client: AsyncClient):
+        """Verify filament can be created."""
+        data = {
+            "name": "New PETG",
+            "type": "PETG",
+            "color": "Blue",
+            "color_hex": "#0000FF",
+            "brand": "Bambu",
+            "cost_per_kg": 30.0,
+        }
+        response = await async_client.post("/api/v1/filaments/", json=data)
+        assert response.status_code == 200
+        result = response.json()
+        assert result["name"] == "New PETG"
+        assert result["type"] == "PETG"
+
+    @pytest.mark.asyncio
+    @pytest.mark.integration
+    async def test_get_filament(
+        self, async_client: AsyncClient, filament_factory, db_session
+    ):
+        """Verify single filament can be retrieved."""
+        filament = await filament_factory(name="Get Test")
+        response = await async_client.get(f"/api/v1/filaments/{filament.id}")
+        assert response.status_code == 200
+        assert response.json()["name"] == "Get Test"
+
+    @pytest.mark.asyncio
+    @pytest.mark.integration
+    async def test_get_filament_not_found(self, async_client: AsyncClient):
+        """Verify 404 for non-existent filament."""
+        response = await async_client.get("/api/v1/filaments/9999")
+        assert response.status_code == 404
+
+    @pytest.mark.asyncio
+    @pytest.mark.integration
+    async def test_update_filament(
+        self, async_client: AsyncClient, filament_factory, db_session
+    ):
+        """Verify filament can be updated."""
+        filament = await filament_factory(name="Original")
+        response = await async_client.patch(
+            f"/api/v1/filaments/{filament.id}",
+            json={"name": "Updated", "cost_per_kg": 35.0}
+        )
+        assert response.status_code == 200
+        result = response.json()
+        assert result["name"] == "Updated"
+        assert result["cost_per_kg"] == 35.0
+
+    @pytest.mark.asyncio
+    @pytest.mark.integration
+    async def test_delete_filament(
+        self, async_client: AsyncClient, filament_factory, db_session
+    ):
+        """Verify filament can be deleted."""
+        filament = await filament_factory()
+        response = await async_client.delete(f"/api/v1/filaments/{filament.id}")
+        assert response.status_code == 200
+        # Verify deleted
+        response = await async_client.get(f"/api/v1/filaments/{filament.id}")
+        assert response.status_code == 404