Race condition in VoiceSentinel report buffer can corrupt transcripts

VoiceSentinel is a real-time voice moderation system for Minecraft servers. From 2.2.1 until 3.3.1, the optional report buffer feature has a race between retention cleanup and normal transcript writes. In `report_buffer.py`, `_maybe_cleanup()` uses an unlocked dictionary for once-per-hour cleanup throttling, allowing simultaneous `_cleanup_tenant()` operations for one tenant. Cleanup reads `transcripts.jsonl` and rewrites it in place without file locking or atomic replacement, while `report_buffer_append_async` uses `asyncio.to_thread` to append without synchronization. In `main.py`, concurrent `_processing_worker` tasks make this reachable in normal operation; `processing.worker_count` of two or more and public-pool servers sharing a `server_key` increase collisions. With `report_buffer.enabled` set to true, racing writes can lose, duplicate or corrupt transcript data and defeat `report_buffer.retention_seconds` pruning, allowing unbounded disk growth that can exhaust storage and crash the host or other services sharing it. The feature is opt-in and disabled by default. This issue is fixed in version 3.3.1.