Extract store helpers into storage_helpers.py

auto_out_path, load_store, save_store moved out of data_model.py into
their own module. data_model.py now contains only value helpers and
domain extractors.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

collect.py

@@ -58,7 +58,8 @@ from pathlib import Path
 import log_config
 import network
 import we_connect
-from data_model import ALL_DOMAINS, auto_out_path, collect_snapshot, load_store, save_store
+from data_model import ALL_DOMAINS, collect_snapshot
+from storage_helpers import auto_out_path, load_store, save_store
 
 log = logging.getLogger(__name__)