* Introduce weed shell command `ec.check.replication`.
This command performs a quick check of EC volume shard replication, reporting
volumes whose shards are over- or under-replicated. Each volume is checked
against its own data+parity ratio, obtained via
erasure_coding.EcShardsVolume{Data,Parity}Shards, so builds that derive the EC
ratio per volume report custom ratios correctly.
The name follows the shell's convention (cluster.check, volume.check.disk); the
closest normal-volume counterpart is volume.fix.replication.
* shell: ec.check.replication reports mixed under+over-replication in both lists