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