fix: add COPY --from=lint to builder stage to force lint execution

BuildKit skips unreferenced stages silently. The lint stage was never
referenced by the builder stage via COPY --from, so it was being skipped
entirely during docker build. This adds a stage dependency that forces
the lint stage to complete before the build proceeds.

closes #153

Dockerfile

@@ -15,6 +15,9 @@ RUN make lint
 # golang:1.25-alpine
 FROM golang@sha256:f6751d823c26342f9506c03797d2527668d095b0a15f1862cddb4d927a7a4ced AS builder
 
+# Force BuildKit to run the lint stage by creating a stage dependency
+COPY --from=lint /src/go.sum /dev/null
+
 RUN apk add --no-cache git make gcc musl-dev
 
 WORKDIR /src