refactor(docker): improve Docker setup and reduce image size

- Add multi-stage build to Dockerfile for smaller production image
- Move docker-compose.yml to project root for easier usage
- Flatten docker/init/setup.sh to docker/setup.sh
- Expand .dockerignore to exclude unnecessary files
- Remove deprecated version field from compose files

Dockerfile

@@ -1,4 +1,5 @@
-FROM golang:1.25-alpine3.21
+# Build stage
+FROM golang:1.25-alpine3.21 AS builder
 
 ENV GO111MODULE=on
 
@@ -11,4 +12,16 @@ RUN go mod download
 
 COPY . .
 
-CMD [ "go", "run", "." ]
+RUN CGO_ENABLED=0 GOOS=linux go build -o erupe-ce .
+
+# Runtime stage
+FROM alpine:3.21
+
+RUN apk --no-cache add ca-certificates tzdata
+
+WORKDIR /app/erupe
+
+COPY --from=builder /app/erupe/erupe-ce .
+
+# Default command runs the compiled binary
+CMD [ "./erupe-ce" ]