Adds .forgejo/workflows/release.yml: triggered by tag push or
workflow_dispatch, it validates the tag/CHANGELOG parity (stable /
preview / unstable), builds the PostIt Android APK via the existing
Dockerfile (--target build-env), and publishes a Forgejo release with
the APK as an asset via rasterstate/forgejo-release-action@v1.
Mirrors the validate-release logic of .github/workflows/docker-publish-android.yml
so the two channels (Forgejo source-of-truth + GitHub mirror) stay
consistent. Authentication uses ${{ secrets.RELEASE_TOKEN }}, a Forgejo
PAT scoped to write:repository configured in the repository's Actions
secrets.
