fix: update test fixtures for SQLite storage migration

All store tests were passing file paths instead of Database objects
after the JSON-to-SQLite migration. Updated fixtures to create temp
Database instances, rewrote backup e2e tests for binary .db format,
and fixed config tests for the simplified StorageConfig.

server/tests/api/routes/test_devices_routes.py

@@ -30,13 +30,21 @@ def _make_app():
 
 
 @pytest.fixture
-def device_store(tmp_path):
-    return DeviceStore(tmp_path / "devices.json")
+def _route_db(tmp_path):
+    from wled_controller.storage.database import Database
+    db = Database(tmp_path / "test.db")
+    yield db
+    db.close()
 
 
 @pytest.fixture
-def output_target_store(tmp_path):
-    return OutputTargetStore(str(tmp_path / "output_targets.json"))
+def device_store(_route_db):
+    return DeviceStore(_route_db)
+
+
+@pytest.fixture
+def output_target_store(_route_db):
+    return OutputTargetStore(_route_db)
 
 
 @pytest.fixture