update environment configuration, enhance setup guide, and align documentation with new domain structure

backend/playout/Dockerfile

@@ -1,8 +1,7 @@
-FROM golang:1.23-alpine AS builder
+FROM golang:1.25-alpine AS builder
 
 WORKDIR /app
 COPY src/ ./src/
-COPY go.mod go.sum ./
 
 # Initialize Go module if not present
 RUN go mod init playout || true

backend/playout/src/playlist.go

@@ -75,7 +75,7 @@ func ValidateVideo(videoPath string) (VideoFile, error) {
 	v := VideoFile{Path: videoPath}
 
 	cmd := exec.Command("ffprobe", "-v", "quiet", "-print_format", "json", "-show_format", "-show_streams", videoPath)
-	output, err := cmd.Output()
+		_, err := cmd.Output()
 	if err != nil {
 		v.Validation = "ffprobe failed: " + err.Error()
 		return v, err