Deploy workflow: commit-id image tags, guarded deploy.sh, opt-in prune

- Makefile builds from 'git archive HEAD' (stale-remote-HEAD impossible):
  tags registry.tanshu.com/mozimo:<short-commit> + :main; build-check target
  verifies both architectures without pushing
- deploy.sh: refuses dirty tracked tree / HEAD != origin/main (--force to
  bypass), ff-only pull, passes the commit as image_tag to ansible,
  --prune flag for opt-in image cleanup
- ansible: docker_image uses image_tag extra-var (falls back to tag),
  prune task keeps the 3 newest mozimo images, mozimo-repo only

deploy.sh

@@ -1,14 +1,51 @@
 #!/usr/bin/env bash
+# Mozimo deploy — build the exact commit at origin/main, tag it with its
+# commit id, and hand that tag to ansible. Guards make it impossible to
+# deploy anything other than what git knows about.
+#
+#   ./deploy.sh           deploy HEAD (must be pushed, tree must be clean)
+#   ./deploy.sh --prune   also drop old mozimo images on the server (keep 3)
+#   ./deploy.sh --force   skip the guards (know what you are doing)
 set -euo pipefail
-parent_path=$( cd "$(dirname "${BASH_SOURCE[0]}")" || exit ; pwd -P )
-cd "$parent_path" || exit
-git pull
-if [ 1 -eq "$#" ]
-then
-  make build-production TAG="$1"
-else
-  make build-production
+cd "$(dirname "${BASH_SOURCE[0]}")"
+
+FORCE=false
+PRUNE=false
+for arg in "$@"; do
+	case "$arg" in
+	--force) FORCE=true ;;
+	--prune) PRUNE=true ;;
+	*)
+		echo "Usage: $0 [--force] [--prune]"
+		exit 1
+		;;
+	esac
+done
+
+# guards: only tracked-file state matters (untracked files never enter a
+# `git archive HEAD` build); HEAD must equal origin/main
+if [ "$FORCE" != true ]; then
+	if [ -n "$(git status --porcelain --untracked-files=no)" ]; then
+		echo "✗ tracked files modified — commit or stash first (or --force)" >&2
+		exit 1
+	fi
+	git fetch origin --quiet
+	if [ "$(git rev-parse HEAD)" != "$(git rev-parse origin/main)" ]; then
+		echo "✗ HEAD != origin/main — push or pull first (or --force)" >&2
+		exit 1
+	fi
 fi
 
-cd "$parent_path/ansible" || exit
-ansible-playbook playbook.yml
+git pull --ff-only
+TAG=$(git rev-parse --short HEAD)
+echo "▶ deploying commit $TAG"
+make build-production TAG="$TAG"
+
+PRUNE_FLAG=""
+if [ "$PRUNE" = true ]; then
+	PRUNE_FLAG="-e mozimo_image_prune=true"
+fi
+
+cd ansible
+# shellcheck disable=SC2086
+ansible-playbook playbook.yml -e "image_tag=$TAG" $PRUNE_FLAG