fix(lists): deleteOwnedList unserialized, can race with item mutations #7725

Summary

deleteOwnedList is not serialized through the per-list operation lane, allowing concurrent mutations that can corrupt the deletion state.

Root Cause

• _serializeListOperation exists for all other mutations (line 110)
• deleteOwnedList (line 698) does not call it
• Concurrent item mutations + delete can interleave
• Delete publishes NIP-09 deletion, but concurrent item add is not blocked

Impact

• Race condition: Item added while deletion is in flight
• Inconsistent state: Item exists locally but deletion says it's gone
• User-visible bug: Item re-appears after user confirms deletion

Technical Details

• deleteOwnedList calls _publishListToNostr directly without serialization
• _serializeListOperation usage pattern established in _createList, _commitListMutation, _updateList
• Missing await on serialization lane allows interleaving

Required Fixes

1. Wrap deleteOwnedList logic in _serializeListOperation
2. Add test: concurrent delete + item add produces consistent state
3. Verify NIP-09 deletion publishes after all pending mutations complete