fix: resolve remaining lint issues and exclude .claude folder

- Fix gosimple S1009: remove unnecessary nil checks before len()
- Fix errcheck: handle avcodec.PacketRef error
- Add .claude/** to git-copy exclusions

Author: obinnaokechukwu

decoder.go

@@ -239,7 +239,7 @@ func NewDecoderWithOptions(path string, opts *DecoderOptions) (*Decoder, error)
 
 	// Stream selection.
 	wantVideo, wantAudio := true, true
-	if opts != nil && len(opts.Streams) > 0 {
+	if len(opts.Streams) > 0 {
 		wantVideo, wantAudio = false, false
 		for _, mt := range opts.Streams {
 			switch mt {

remuxer.go

@@ -72,7 +72,7 @@ func NewRemuxer(outputPath string, decoder *Decoder, cfg *RemuxerConfig) (*Remux
 
 	// Determine which streams to copy
 	var streamsToCopy []int
-	if cfg != nil && len(cfg.InputStreams) > 0 {
+	if len(cfg.InputStreams) > 0 {
 		streamsToCopy = cfg.InputStreams
 	} else {
 		// Copy all streams
@@ -210,7 +210,7 @@ func (r *Remuxer) WritePacket(pkt avcodec.Packet, inputStreamIdx int) error {
 	}
 
 	// Reference the packet (don't copy data, just increment refcount)
-	avcodec.PacketRef(r.packet, pkt)
+	_ = avcodec.PacketRef(r.packet, pkt)
 
 	// Set output stream index
 	avcodec.SetPacketStreamIndex(r.packet, int32(outputIdx))