WAL writes now go through bufio.Writer instead of raw syscalls per record,
reducing I/O overhead. Buffers are flushed on rotate, drain, and shutdown.
Fixed misleading MemoryCap comment ("Max bytes" → "Max memory in GB").
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Entire-Checkpoint: b38dc35e5334