ci(docker): add Docker publishing workflow and Dockerfile

Introduce GitHub Actions workflow for automated Docker image
publishing to Docker Hub, along with a dedicated Dockerfile in
the ci directory to streamline container builds.

.github/workflows/docker-publish.yml

@@ -0,0 +1,54 @@
+name: Publish Docker image
+
+on:
+  push:
+    branches: [master,  ci/docker-hub-publishing]
+  release:
+    types: [published]
+
+jobs:
+  push_to_registry:
+    name: Push Docker image to Docker Hub
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+      contents: read
+      attestations: write
+      id-token: write
+    steps:
+      - name: Check out the repo
+        uses: actions/checkout@v7
+
+      - name: Log in to Docker Hub
+        uses: docker/login-action@f4ef78c080cd8ba55a85445d5b36e214a81df20a
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@9ec57ed1fcdbf14dcef7dfbe97b2010124a938b7
+        with:
+          images: cproofdev/cproof
+          tags: |
+            type=raw,value=dev,enable-if-ref=refs/heads/master
+            type=sha,prefix=nightly-,enable-if-ref=refs/heads/master
+            type=ref,event=tag
+            type=raw,value=latest,enable-if-ref=refs/tags/*
+
+      - name: Build and push Docker image
+        id: push
+        uses: docker/build-push-action@3b5e8027fcad23fda98b2e3ac259d8d67585f671
+        with:
+          context: .
+          file: ./ci/Dockerfile
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+
+      - name: Generate artifact attestation
+        uses: actions/attest@v4
+        with:
+          subject-name: index.docker.io/cproofdev/cproof
+          subject-digest: ${{ steps.push.outputs.digest }}
+          push-to-registry: true