build: stamp git metadata into the container image

.containerignore excludes .git, so go build's automatic VCS stamping produced
nothing and telesrv logged git_commit/git_branch/git_tree_state/build_time as
"unknown" on startup.

- Containerfile: accept GIT_COMMIT/GIT_BRANCH/GIT_TREE_STATE/BUILD_TIME build
  args and pass them to the gramsrv build via -ldflags -X.
- build.sh: wrapper that fills those args from the current checkout and runs
  podman build.

Containerfile

@@ -1,7 +1,22 @@
 FROM docker.io/library/golang:1.25 AS build
+# Build metadata for telesrv's startup log (git_commit/git_branch/... in
+# cmd/telesrv/buildinfo.go). .containerignore excludes .git, so go build's
+# automatic VCS stamping sees no repo; pass these in explicitly, e.g.:
+#   podman build \
+#     --build-arg GIT_COMMIT="$(git rev-parse HEAD)" \
+#     --build-arg GIT_BRANCH="$(git rev-parse --abbrev-ref HEAD)" \
+#     --build-arg GIT_TREE_STATE="$(git diff --quiet && echo clean || echo dirty)" \
+#     --build-arg BUILD_TIME="$(date -u +%Y-%m-%dT%H:%M:%SZ)" \
+#     -t owpengram-server -f Containerfile .
+ARG GIT_COMMIT=unknown
+ARG GIT_BRANCH=unknown
+ARG GIT_TREE_STATE=unknown
+ARG BUILD_TIME=unknown
 WORKDIR /src
 COPY . .
-RUN CGO_ENABLED=0 go build -trimpath -o /out/gramsrv ./cmd/telesrv
+RUN CGO_ENABLED=0 go build -trimpath \
+    -ldflags "-X main.gitCommit=${GIT_COMMIT} -X main.gitBranch=${GIT_BRANCH} -X main.gitTreeState=${GIT_TREE_STATE} -X main.buildTime=${BUILD_TIME}" \
+    -o /out/gramsrv ./cmd/telesrv
 RUN CGO_ENABLED=0 go build -trimpath -o /out/telesrv-admin ./cmd/telesrv-admin
 
 FROM docker.io/library/alpine:3.20

build.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Build the owpengram-server container image, stamping the current git state
+# into the binary (shows up in telesrv's startup log as git_commit/git_branch/
+# git_tree_state/build_time). .containerignore excludes .git, so go build's
+# automatic VCS stamping can't see the repo - the values are passed in here.
+#
+# Usage:  ./build.sh [extra podman build args...]
+#   IMAGE=my/tag ./build.sh            # override the image tag (default: owpengram-server)
+set -euo pipefail
+cd "$(dirname "$0")"
+
+IMAGE="${IMAGE:-owpengram-server}"
+
+podman build \
+  --build-arg GIT_COMMIT="$(git rev-parse HEAD)" \
+  --build-arg GIT_BRANCH="$(git rev-parse --abbrev-ref HEAD)" \
+  --build-arg GIT_TREE_STATE="$(git diff --quiet && echo clean || echo dirty)" \
+  --build-arg BUILD_TIME="$(date -u +%Y-%m-%dT%H:%M:%SZ)" \
+  -t "$IMAGE" \
+  -f Containerfile \
+  "$@" \
+  .