CI: migrate release workflow from GitHub Actions to Forgejo Actions

GitHub Actions self-hosted runners need per-repo registration on a
personal account; Forgejo Actions' runner already serves every repo
with zero setup. Moves release publishing there (dl.breadway.dev stays
the primary bakery target; GitHub release upload is kept as the
fallback via an explicit token, since Forgejo Actions has no ambient
GITHUB_TOKEN) and adds a mirror workflow to keep GitHub in sync
automatically.

.github/workflows/release.yml

@@ -1,58 +0,0 @@
-name: release
-
-on:
-  push:
-    tags: ["v*"]
-
-permissions:
-  contents: write
-
-env:
-  DL_DIR: /srv/breadway-dl
-  ECOSYSTEM_DIR: /tmp/bread-ecosystem-ci
-
-jobs:
-  build:
-    runs-on: [self-hosted, hestia]
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: build
-        run: cargo build --release --locked
-
-      - name: test
-        run: cargo test --release --locked
-
-      - name: prepare artifacts
-        run: |
-          VERSION="${GITHUB_REF_NAME#v}"
-          PKG_DIR="${DL_DIR}/breadcrumbs/${VERSION}"
-          mkdir -p "${PKG_DIR}"
-          cp target/release/breadcrumbs "${PKG_DIR}/breadcrumbs-x86_64"
-          strip "${PKG_DIR}/breadcrumbs-x86_64"
-          sha256sum "${PKG_DIR}/breadcrumbs-x86_64" | awk '{print $1}' \
-            > "${PKG_DIR}/breadcrumbs-x86_64.sha256"
-          cp breadcrumbs.example.toml "${PKG_DIR}/"
-          cp bakery.toml "${PKG_DIR}/bakery.toml"
-          ln -sfn "${VERSION}" "${DL_DIR}/breadcrumbs/latest"
-
-      - name: ensure bread-ecosystem
-        run: |
-          rm -rf "${ECOSYSTEM_DIR}"
-          git clone https://github.com/Breadway/bread-ecosystem.git "${ECOSYSTEM_DIR}"
-
-      - name: regenerate index.json
-        run: bash "${ECOSYSTEM_DIR}/scripts/gen-index.sh"
-
-      - name: upload to GitHub Release
-        env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        run: |
-          VERSION="${GITHUB_REF_NAME#v}"
-          PKG_DIR="${DL_DIR}/breadcrumbs/${VERSION}"
-          gh release create "${GITHUB_REF_NAME}" \
-            --title "breadcrumbs v${VERSION}" --generate-notes 2>/dev/null || true
-          gh release upload "${GITHUB_REF_NAME}" \
-            "${PKG_DIR}/breadcrumbs-x86_64" \
-            "${PKG_DIR}/breadcrumbs-x86_64.sha256" \
-            --clobber