ci: allow manual semver image publishing

.woodpecker/release-backend.yml

@@ -1,6 +1,7 @@
 when:
   - event: tag
     ref: refs/tags/v*
+  - event: manual
 
 labels:
   ci: domain-linux-native
@@ -18,7 +19,9 @@ steps:
   release-checks:
     image: bash
     commands:
-      - node scripts/check-api-contract.mjs "$CI_COMMIT_TAG"
+      - release_tag="${CI_COMMIT_TAG:-${RELEASE_TAG:-}}"
+      - test -n "$release_tag"
+      - node scripts/check-api-contract.mjs "$release_tag"
       - dotnet test server/WebDrop.slnx --configuration Release --verbosity minimal
 
   publish-backend:
@@ -31,8 +34,10 @@ steps:
       ZOT_REGISTRY: zot.oeo.one
     commands:
       - set -euo pipefail
+      - release_tag="${CI_COMMIT_TAG:-${RELEASE_TAG:-}}"
+      - test -n "$release_tag"
       - printf '%s' "$ZOT_PASSWORD" | buildah login "$ZOT_REGISTRY" --username "$ZOT_USERNAME" --password-stdin
       - trap 'buildah logout "$ZOT_REGISTRY" >/dev/null 2>&1 || true' EXIT
-      - image="$ZOT_REGISTRY/justme/webdrop-api:$CI_COMMIT_TAG"
+      - image="$ZOT_REGISTRY/justme/webdrop-api:$release_tag"
       - buildah bud --format docker --platform linux/amd64 --tag "$image" --file server/Dockerfile .
       - buildah push "$image" "docker://$image"