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/e2e/conftest.py

@@ -46,10 +46,12 @@ def client(_test_client):
 
 def _clear_stores():
     """Remove all entities from all stores for test isolation."""
-    # Reset the saves-frozen flag that freeze_saves() sets during restore flows.
-    # Without this, subsequent tests can't persist data because _save() is a no-op.
+    # Reset frozen-writes flags that restore flows set.
+    # Without this, subsequent tests can't persist data.
     from wled_controller.storage.base_store import unfreeze_saves
     unfreeze_saves()
+    import wled_controller.storage.database as _db_mod
+    _db_mod._writes_frozen = False
 
     from wled_controller.api import dependencies as deps