Install git in the Go build stage for the GOPROXY direct fallback

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Dockerfile

@@ -12,6 +12,8 @@ ARG VERSION=dev
 RUN TEFTER_VERSION=$VERSION npx vite build
 
 FROM docker.io/library/golang:1.25-alpine AS build
+# git enables the GOPROXY "direct" fallback (fetch modules from their VCS).
+RUN apk add --no-cache git
 # Overridable for hosts where proxy.golang.org (Google) is unreachable —
 # set e.g. GOPROXY=https://goproxy.io,direct in .env.docker. Module
 # integrity is still verified against the committed go.sum either way.