feat: add stats helper service

Periodically snapshots Gitea instance metrics from a read-only MySQL
user and writes stats.json into Gitea custom/public/assets for the
home page to fetch same-origin. Config via env vars only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

publish.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Build and publish the stats helper image to the Gitea container registry.
+#
+#   IMAGE=git.hangman-lab.top/hzhang/gitea-stats TAG=0.1.0 ./publish.sh
+#
+# Requires: docker logged in to the registry
+#   echo "$PASSWORD" | docker login git.hangman-lab.top -u hzhang --password-stdin
+set -euo pipefail
+
+IMAGE="${IMAGE:-git.hangman-lab.top/hzhang/gitea-stats}"
+TAG="${TAG:-latest}"
+CONTEXT="$(cd "$(dirname "${BASH_SOURCE[0]}")/stats" && pwd)"
+
+echo "building ${IMAGE}:${TAG} (and :latest) from ${CONTEXT}"
+docker build -t "${IMAGE}:${TAG}" -t "${IMAGE}:latest" "${CONTEXT}"
+
+echo "pushing ${IMAGE}:${TAG}"
+docker push "${IMAGE}:${TAG}"
+echo "pushing ${IMAGE}:latest"
+docker push "${IMAGE}:latest"
+
+echo "done: ${IMAGE}:${TAG}"