refactor: use EcShardConfig message instead of separate fields

weed/pb/volume_server.proto

@@ -525,8 +525,13 @@ message VolumeInfo {
     int64 dat_file_size = 5; // store the original dat file size
     uint64 expire_at_sec = 6; // expiration time of ec volume
     bool read_only = 7;
-    uint32 data_shards_count = 8; // EC data shards (0 = use default 10)
-    uint32 parity_shards_count = 9; // EC parity shards (0 = use default 4)
+    EcShardConfig ec_shard_config = 8; // EC shard configuration (optional, null = use default 10+4)
+}
+
+// EcShardConfig specifies erasure coding shard configuration
+message EcShardConfig {
+    uint32 data_shards = 1;   // Number of data shards (e.g., 10)
+    uint32 parity_shards = 2; // Number of parity shards (e.g., 4)
 }
 message OldVersionVolumeInfo {
     repeated RemoteFile files = 1;

weed/server/volume_grpc_erasure_coding.go

@@ -90,8 +90,10 @@ func (vs *VolumeServer) VolumeEcShardsGenerate(ctx context.Context, req *volume_
 	volumeInfo.DatFileSize = int64(datSize)
 
 	// Save EC configuration to VolumeInfo
-	volumeInfo.DataShardsCount = uint32(ecCtx.DataShards)
-	volumeInfo.ParityShardsCount = uint32(ecCtx.ParityShards)
+	volumeInfo.EcShardConfig = &volume_server_pb.EcShardConfig{
+		DataShards:   uint32(ecCtx.DataShards),
+		ParityShards: uint32(ecCtx.ParityShards),
+	}
 
 	if err := volume_info.SaveVolumeInfo(baseFileName+".vif", volumeInfo); err != nil {
 		return nil, fmt.Errorf("SaveVolumeInfo %s: %v", baseFileName, err)