fix: resolve test pollution from freeze_saves and fix os_listener toggle

- Add unfreeze_saves() to base_store.py and call it in e2e cleanup.
  The backup restore flow calls freeze_saves() which sets a module-level
  flag that silently disables all store _save() calls. Without reset,
  this poisoned all subsequent persistence tests (9 failures).
- Fix os_listener toggle to use toggle-switch/toggle-slider CSS classes
  instead of nonexistent switch/slider classes (was showing plain checkbox).
- Add mandatory test run to CLAUDE.md pre-commit checks.

All 341 tests now pass.

server/tests/e2e/conftest.py

@@ -46,6 +46,11 @@ 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.
+    from wled_controller.storage.base_store import unfreeze_saves
+    unfreeze_saves()
+
     from wled_controller.api import dependencies as deps
 
     store_clearers = [