optimize: simplify VolumeEcShardsToVolume to use existing EC context

- Remove redundant CollectEcShards call
- Remove redundant .vif file loading
- Use v.ECContext.DataShards directly (already loaded by NewEcVolume)
- Slice tempShards instead of collecting again

weed/server/volume_grpc_erasure_coding.go

@@ -453,40 +453,30 @@ func (vs *VolumeServer) VolumeEcShardsToVolume(ctx context.Context, req *volume_
 
 	glog.V(0).Infof("VolumeEcShardsToVolume: %v", req)
 
-	// collect data shard files; derive shard count from .vif if present
-	dataShards := erasure_coding.DataShardsCount
-	
-	// Try to get the volume first to determine data base filename
+	// Collect all EC shards (NewEcVolume will load EC config from .vif into v.ECContext)
 	tempShards := make([]string, erasure_coding.TotalShardsCount)
 	v, found := vs.store.CollectEcShards(needle.VolumeId(req.VolumeId), tempShards)
 	if !found {
 		return nil, fmt.Errorf("ec volume %d not found", req.VolumeId)
 	}
-	
-	dataBaseFileName, indexBaseFileName := v.DataBaseFileName(), v.IndexBaseFileName()
-	
-	// Read EC config from .vif if available
-	if vi, _, found, _ := volume_info.MaybeLoadVolumeInfo(dataBaseFileName + ".vif"); found && vi.EcShardConfig != nil {
-		dataShards = int(vi.EcShardConfig.DataShards)
-		glog.V(1).Infof("Using EC config from VolumeInfo: %d data shards", dataShards)
-	}
-	
-	// Collect only the data shards needed
-	shardFileNames := make([]string, dataShards)
-	v, found = vs.store.CollectEcShards(needle.VolumeId(req.VolumeId), shardFileNames)
-	if !found {
-		return nil, fmt.Errorf("ec volume %d not found", req.VolumeId)
-	}
 
 	if v.Collection != req.Collection {
 		return nil, fmt.Errorf("existing collection:%v unexpected input: %v", v.Collection, req.Collection)
 	}
 
+	// Use EC context (already loaded from .vif) to determine data shard count
+	dataShards := v.ECContext.DataShards
+	shardFileNames := tempShards[:dataShards]
+	glog.V(1).Infof("Using EC config from volume %d: %d data shards", req.VolumeId, dataShards)
+
+	// Verify all data shards are present
 	for shardId := 0; shardId < dataShards; shardId++ {
 		if shardFileNames[shardId] == "" {
 			return nil, fmt.Errorf("ec volume %d missing shard %d", req.VolumeId, shardId)
 		}
 	}
+	
+	dataBaseFileName, indexBaseFileName := v.DataBaseFileName(), v.IndexBaseFileName()
 	// calculate .dat file size
 	datFileSize, err := erasure_coding.FindDatFileSize(dataBaseFileName, indexBaseFileName)
 	if err != nil {