ci: add Docker build and push workflow

- Build and push to DockerHub on main branch pushes and version tags
- Support multi-platform builds (amd64, arm64)
- Automatic semantic versioning (v1.2.3 -> 1.2.3, 1.2, 1)
- Generate build provenance attestations for supply chain security

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: MatteoMori

.github/workflows/build-and-push.yaml

@@ -0,0 +1,85 @@
+name: Build and Push Docker Image
+
+on:
+  push:
+    branches:
+      - main
+    tags:
+      - 'v*.*.*'  # Triggers on version tags like v1.0.0, v1.2.3, etc.
+  pull_request:
+    branches:
+      - main
+
+env:
+  DOCKER_IMAGE: matteomori/sentinel
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.23'
+          cache: true
+
+      - name: Run tests
+        run: go test -v ./...
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to DockerHub
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels)
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.DOCKER_IMAGE }}
+          tags: |
+            # Tag as 'latest' for pushes to main branch
+            type=raw,value=latest,enable={{is_default_branch}}
+            # Tag with git tag (v1.2.3 -> 1.2.3)
+            type=semver,pattern={{version}}
+            # Tag with major.minor (v1.2.3 -> 1.2)
+            type=semver,pattern={{major}}.{{minor}}
+            # Tag with major version (v1.2.3 -> 1)
+            type=semver,pattern={{major}}
+            # Tag with short SHA for commits
+            type=sha,prefix=sha-,format=short
+            # Tag with branch name for non-main branches
+            type=ref,event=branch
+            # Tag with PR number for pull requests
+            type=ref,event=pr
+
+      - name: Build and push Docker image
+        id: build
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+          platforms: linux/amd64,linux/arm64
+
+      - name: Generate artifact attestation
+        if: github.event_name != 'pull_request'
+        uses: actions/attest-build-provenance@v1
+        with:
+          subject-name: ${{ env.DOCKER_IMAGE }}
+          subject-digest: ${{ steps.build.outputs.digest }}
+          push-to-registry: true