ci: harden docker/release/nightly GitHub Actions workflows

- buildx: adopt docker/metadata-action for image tags (replaces hand-rolled shell), add gha build cache, concurrency control, explicit checkout, and least-privilege permissions

- release: add explicit permissions and concurrency (no cancel-in-flight); drop dead UPX install step (disabled in .goreleaser.yaml, see #863)

- trigger-nightly: add concurrency, replace archived dev-drprasad/delete-older-releases with native gh, and harden the 24h commit check

.github/workflows/buildx.yml

@@ -3,57 +3,49 @@
 
 name: docker
 
-on: 
+on:
   push:
     branches:
     - master
     tags:
     - 'v*'
 
+permissions:
+  contents: read
+
+# New pushes cancel an in-progress build for the same ref. Tags are isolated
+# by ref, so re-pushing a release tag only de-dupes itself, never another tag.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - name: Prepare
-      id: prepare
-      run: |
-        DOCKER_IMAGE=${{ secrets.DOCKER_IMAGE }}
-        VERSION=latest
+    - name: Checkout
+      uses: actions/checkout@v4
 
-        # If this is git tag, use the tag name as a docker tag
-        if [[ $GITHUB_REF == refs/tags/* ]]; then
-          VERSION=${GITHUB_REF#refs/tags/v}
-        fi
-        TAGS="${DOCKER_IMAGE}:${VERSION}"
-
-        # If the VERSION looks like a version number, assume that
-        # this is the most recent version of the image and also
-        # tag it 'latest'.
-        if [[ $VERSION =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
-          MAJOR_VERSION=`echo $VERSION | awk '{split($0,a,"."); print a[1]}'`
-          MINOR_VERSION=`echo $VERSION | awk '{split($0,a,"."); print a[2]}'`
-          TAGS="$TAGS,${DOCKER_IMAGE}:${MAJOR_VERSION},${DOCKER_IMAGE}:${MAJOR_VERSION}.${MINOR_VERSION},${DOCKER_IMAGE}:latest"
-        fi
-
-        # Set output parameters.
-        echo "tags=${TAGS}" >> $GITHUB_OUTPUT
-        echo "docker_image=${DOCKER_IMAGE}" >> $GITHUB_OUTPUT
-        echo "docker_platforms=linux/386,linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64/v8,linux/s390x,linux/riscv64" >> $GITHUB_OUTPUT
+    # Auto-generates image tags, replacing the former hand-rolled shell:
+    #   - master push                         -> :latest
+    #   - clean release tag vX.Y.Z             -> :X.Y.Z :X :X.Y :latest
+    #   - nightly tag vX.Y.Z-nightly.<date>    -> :X.Y.Z-nightly.<date>   (no major/minor/latest)
+    - name: Docker meta
+      id: meta
+      uses: docker/metadata-action@v5
+      with:
+        images: ${{ secrets.DOCKER_IMAGE }}
+        flavor: latest=false
+        tags: |
+          type=raw,value=latest,enable=${{ github.ref == format('refs/heads/{0}', github.event.repository.default_branch) || (startsWith(github.ref, 'refs/tags/v') && !contains(github.ref_name, '-')) }}
+          type=semver,pattern={{version}}
+          type=semver,pattern={{major}},enable=${{ !contains(github.ref_name, '-') }}
+          type=semver,pattern={{major}}.{{minor}},enable=${{ !contains(github.ref_name, '-') }}
 
     - name: Set up Docker Buildx
       id: buildx
       uses: docker/setup-buildx-action@v3
 
-    - name: Environment
-      run: |
-        echo home=$HOME
-        echo git_ref=$GITHUB_REF
-        echo git_sha=$GITHUB_SHA
-        echo image=${{ steps.prepare.outputs.docker_image }}
-        echo tags=${{ steps.prepare.outputs.tags }}
-        echo platforms=${{ steps.prepare.outputs.docker_platforms }}
-        echo avail_platforms=${{ steps.buildx.outputs.platforms }}
-
     - name: Login to DockerHub
       if: github.event_name != 'pull_request'
       uses: docker/login-action@v3
@@ -64,6 +56,9 @@ jobs:
     - name: Buildx and push
       uses: docker/build-push-action@v6
       with:
-        platforms: ${{ steps.prepare.outputs.docker_platforms }}
+        platforms: linux/386,linux/amd64,linux/arm/v6,linux/arm/v7,linux/arm64/v8,linux/s390x,linux/riscv64
         push: true
-        tags: ${{ steps.prepare.outputs.tags }}
+        tags: ${{ steps.meta.outputs.tags }}
+        # Reuse build layers across runs via the GitHub Actions cache.
+        cache-from: type=gha
+        cache-to: type=gha,mode=max