Copy go.sum into the Docker build; pin compose example to v0.1.5

The image build broke with the first Linux-imported dependency
(go-systemd): the Dockerfile copied go.mod only, and the missing go.sum
never mattered while golang.org/x/sys was Windows-only.

Dockerfile

@@ -1,6 +1,6 @@
 FROM golang:1.23 AS build
 WORKDIR /src
-COPY go.mod ./
+COPY go.mod go.sum ./
 COPY cmd ./cmd
 COPY internal ./internal
 ARG VERSION=dev

compose.yaml.example

@@ -6,7 +6,7 @@
 # ComfyUI --listen 0.0.0.0 --port 8189).
 services:
   gpu-turnstile:
-    image: git.rambossek.at/public/gpu-turnstile:v0.1.4
+    image: git.rambossek.at/public/gpu-turnstile:v0.1.5
     restart: unless-stopped
     environment:
       # Each consumer is enabled by setting its URL; leave one unset to