ec: allow disk type fallback during evacuation

Update pickBestDiskOnNode to accept a strictDiskType parameter:

- strictDiskType=true (balancing): Only use disks of matching type.
  This maintains storage tier isolation during normal rebalancing.

- strictDiskType=false (evacuation): Prefer same disk type, but
  fall back to other disk types if no matching disk is available.
  This ensures evacuation can complete even when same-type capacity
  is insufficient.

Priority order for evacuation:
1. Same disk type with lowest shard count (preferred)
2. Different disk type with lowest shard count (fallback)

weed/shell/command_volume_server_evacuate.go

@@ -165,14 +165,14 @@ func (c *commandVolumeServerEvacuate) evacuateEcVolumes(commandEnv *CommandEnv,
 
 	for _, diskType := range diskTypes {
 		ecNodes, _ := collectEcVolumeServersByDc(c.topologyInfo, "", diskType)
-	thisNodes, otherNodes := c.ecNodesOtherThan(ecNodes, volumeServer)
-	if len(thisNodes) == 0 {
+		thisNodes, otherNodes := c.ecNodesOtherThan(ecNodes, volumeServer)
+		if len(thisNodes) == 0 {
 			// This server doesn't have EC shards for this disk type, skip
 			continue
-	}
+		}
 
 		// move away ec volumes for this disk type
-	for _, thisNode := range thisNodes {
+		for _, thisNode := range thisNodes {
 			diskInfo, found := thisNode.info.DiskInfos[string(diskType)]
 			if !found {
 				continue