Compaction OffsetMap fails when hash index is Integer.MIN_VALUE

CompactionLog.OffsetMap uses Math.abs(index) before applying the table capacity. Math.abs(Integer.MIN_VALUE) remains negative, which can produce a negative ByteBuffer position and break compaction lookup. Expected behavior: map every hash value, including Integer.MIN_VALUE, to a valid non-negative entry.

Search for CompactionLog.OffsetMap and inspect how its hash index is converted before the table capacity is applied. Add coverage for Integer.MIN_VALUE and verify that compaction lookup maps it to a valid non-negative entry without producing an invalid ByteBuffer position.

Written by the indexing model from the issue text.