fix: replace TotalShardsCount with MaxShardCount for custom EC ratio support

Critical fixes to support custom EC ratios > 14 shards:

disk_location_ec.go:
- validateEcVolume: Check shards 0-31 instead of 0-13 during validation
- removeEcVolumeFiles: Remove shards 0-31 instead of 0-13 during cleanup

ec_volume_info.go ShardBits methods:
- ShardIds(): Iterate up to MaxShardCount (32) instead of TotalShardsCount (14)
- ToUint32Slice(): Iterate up to MaxShardCount (32)
- IndexToShardId(): Iterate up to MaxShardCount (32)
- MinusParityShards(): Remove shards 10-31 instead of 10-13 (added note about Phase 2)
- Minus() shard size copy: Iterate up to MaxShardCount (32)
- resizeShardSizes(): Iterate up to MaxShardCount (32)

Without these changes:
- Custom EC ratios > 14 total shards would fail validation on startup
- Shards 14-31 would never be discovered or cleaned up
- ShardBits operations would miss shards >= 14

These changes are backward compatible - MaxShardCount (32) includes
the default TotalShardsCount (14), so existing 10+4 volumes work as before.

weed/storage/disk_location_ec.go

@@ -398,8 +398,8 @@ func (l *DiskLocation) validateEcVolume(collection string, vid needle.VolumeId)
 	var actualShardSize int64 = -1
 
 	// Count shards and validate they all have the same size (required for Reed-Solomon EC)
-	// Shard files (.ec00 - .ec13) are always in l.Directory, not l.IdxDirectory
-	for i := 0; i < erasure_coding.TotalShardsCount; i++ {
+	// Check up to MaxShardCount (32) to support custom EC ratios
+	for i := 0; i < erasure_coding.MaxShardCount; i++ {
 		shardFileName := baseFileName + erasure_coding.ToExt(i)
 		fi, err := os.Stat(shardFileName)
 
@@ -472,8 +472,9 @@ func (l *DiskLocation) removeEcVolumeFiles(collection string, vid needle.VolumeI
 	removeFile(indexBaseFileName+".ecx", "EC index file")
 	removeFile(indexBaseFileName+".ecj", "EC journal file")
 
-	// Remove all EC shard files (.ec00 ~ .ec13) from data directory
-	for i := 0; i < erasure_coding.TotalShardsCount; i++ {
+	// Remove all EC shard files (.ec00 ~ .ec31) from data directory
+	// Use MaxShardCount (32) to support custom EC ratios
+	for i := 0; i < erasure_coding.MaxShardCount; i++ {
 		removeFile(baseFileName+erasure_coding.ToExt(i), "EC shard file")
 	}
 }

weed/storage/erasure_coding/ec_volume_info.go

@@ -87,7 +87,7 @@ func (ecInfo *EcVolumeInfo) Minus(other *EcVolumeInfo) *EcVolumeInfo {
 
 	// Copy shard sizes for remaining shards
 	retIndex := 0
-	for shardId := ShardId(0); shardId < TotalShardsCount && retIndex < len(ret.ShardSizes); shardId++ {
+	for shardId := ShardId(0); shardId < MaxShardCount && retIndex < len(ret.ShardSizes); shardId++ {
 		if ret.ShardBits.HasShardId(shardId) {
 			if size, exists := ecInfo.GetShardSize(shardId); exists {
 				ret.ShardSizes[retIndex] = size
@@ -135,7 +135,7 @@ func (b ShardBits) HasShardId(id ShardId) bool {
 }
 
 func (b ShardBits) ShardIds() (ret []ShardId) {
-	for i := ShardId(0); i < TotalShardsCount; i++ {
+	for i := ShardId(0); i < MaxShardCount; i++ {
 		if b.HasShardId(i) {
 			ret = append(ret, i)
 		}
@@ -144,7 +144,7 @@ func (b ShardBits) ShardIds() (ret []ShardId) {
 }
 
 func (b ShardBits) ToUint32Slice() (ret []uint32) {
-	for i := uint32(0); i < TotalShardsCount; i++ {
+	for i := uint32(0); i < MaxShardCount; i++ {
 		if b.HasShardId(ShardId(i)) {
 			ret = append(ret, i)
 		}
@@ -168,7 +168,9 @@ func (b ShardBits) Plus(other ShardBits) ShardBits {
 }
 
 func (b ShardBits) MinusParityShards() ShardBits {
-	for i := DataShardsCount; i < TotalShardsCount; i++ {
+	// Note: This method assumes default 10+4 EC layout where parity shards are IDs 10-31
+	// For custom EC ratios in Phase 2, this would need to accept an ECContext parameter
+	for i := DataShardsCount; i < MaxShardCount; i++ {
 		b = b.RemoveShardId(ShardId(i))
 	}
 	return b
@@ -209,7 +211,7 @@ func (b ShardBits) IndexToShardId(index int) (shardId ShardId, found bool) {
 	}
 
 	currentIndex := 0
-	for i := ShardId(0); i < TotalShardsCount; i++ {
+	for i := ShardId(0); i < MaxShardCount; i++ {
 		if b.HasShardId(i) {
 			if currentIndex == index {
 				return i, true
@@ -238,7 +240,7 @@ func (ecInfo *EcVolumeInfo) resizeShardSizes(prevShardBits ShardBits) {
 	// Copy existing sizes to new positions based on current ShardBits
 	if len(ecInfo.ShardSizes) > 0 {
 		newIndex := 0
-		for shardId := ShardId(0); shardId < TotalShardsCount && newIndex < expectedLength; shardId++ {
+		for shardId := ShardId(0); shardId < MaxShardCount && newIndex < expectedLength; shardId++ {
 			if ecInfo.ShardBits.HasShardId(shardId) {
 				// Try to find the size for this shard in the old array using previous ShardBits
 				if oldIndex, found := prevShardBits.ShardIdToIndex(shardId); found && oldIndex < len(ecInfo.ShardSizes) {