Bake git commit into the binary and log it at startup

New internal/version package: ldflags-stamped Commit with a
debug.ReadBuildInfo VCS fallback for host builds. Startup log line
carries commit + Go version; --version prints the hash and exits.
Makefile computes GIT_COMMIT (12 chars, -dirty on any local change) and
passes it to docker-build/buildx; Dockerfile injects it via -ldflags and
an org.opencontainers.image.revision label. make build now uses ./cmd —
file-argument builds skip Go's automatic VCS stamp.

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

Dockerfile

@@ -2,6 +2,7 @@
 FROM golang:1.26 AS builder
 ARG TARGETOS
 ARG TARGETARCH
+ARG GIT_COMMIT=unknown
 
 WORKDIR /workspace
 # Copy the Go Modules manifests
@@ -19,11 +20,15 @@ COPY . .
 # was called. For example, if we call make docker-build in a local env which has the Apple Silicon M1 SO
 # the docker BUILDPLATFORM arg will be linux/arm64 when for Apple x86 it will be linux/amd64. Therefore,
 # by leaving it empty we can ensure that the container and binary shipped on it will have the same platform.
-RUN CGO_ENABLED=0 GOOS=${TARGETOS:-linux} GOARCH=${TARGETARCH} go build -a -o manager cmd/main.go
+RUN CGO_ENABLED=0 GOOS=${TARGETOS:-linux} GOARCH=${TARGETARCH} go build -a \
+    -ldflags "-X gitea.home.hrajfrisbee.cz/kacerr/egress-proxies-operator/internal/version.Commit=${GIT_COMMIT}" \
+    -o manager cmd/main.go
 
 # Use distroless as minimal base image to package the manager binary
 # Refer to https://github.com/GoogleContainerTools/distroless for more details
 FROM gcr.io/distroless/static:nonroot
+ARG GIT_COMMIT=unknown
+LABEL org.opencontainers.image.revision="${GIT_COMMIT}"
 WORKDIR /
 COPY --from=builder /workspace/manager .
 USER 65532:65532