Fix HIGH issues:
- Fix empty disk discovery: Now discovers all disks from VolumeInfos,
not just from EC shards. This ensures disks without EC shards are
still considered for placement.
- Fix EC shard count calculation in detection.go: Now correctly filters
by DiskId and sums actual shard counts using ShardBits.ShardIdCount()
instead of just counting EcShardInfo entries.
Fix MEDIUM issues:
- Add disk ID to evacuation log messages for consistency with other logging
- Remove unused serverToDisks variable in placement.go
- Fix comment that incorrectly said 'ascending' when sorting is 'descending'