ci: Add GitHub Actions workflow for Docker Hub publication

Add automated Docker image building and publishing:
- Triggers on release publication
- Builds multi-platform images (linux/amd64, linux/arm64)
- Pushes to Docker Hub with semantic versioning tags
- Updates Docker Hub description from README.md

Configuration required:
- DOCKERHUB_USERNAME secret
- DOCKERHUB_TOKEN secret

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

.github/workflows/docker-publish.yml

@@ -0,0 +1,64 @@
+name: Build and Push Docker Image
+
+on:
+  release:
+    types: [published]
+  workflow_dispatch:
+
+env:
+  REGISTRY: docker.io
+  IMAGE_NAME: ${{ secrets.DOCKERHUB_USERNAME }}/tidyquest
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Docker Hub
+        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.IMAGE_NAME }}
+          tags: |
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=semver,pattern={{major}}
+            type=raw,value=latest,enable={{is_default_branch}}
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+      - name: Update Docker Hub description
+        uses: peter-evans/dockerhub-description@v4
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+          repository: ${{ secrets.DOCKERHUB_USERNAME }}/tidyquest
+          short-description: "Transform household chores into an epic family adventure - Self-hosted gamification app"
+          readme-filepath: ./README.md