ci: add GitHub workflow for Docker image build and push

Co-authored-by: aider (anthropic/claude-sonnet-4-20250514) <[email protected]>

Author: XanderStrike

.github/workflows/docker.yml

@@ -0,0 +1,57 @@
+name: Build and Push Docker Image
+
+on:
+  push:
+    branches: [ main ]
+    tags: [ 'v*' ]
+  pull_request:
+    branches: [ main ]
+
+env:
+  REGISTRY: docker.io
+  IMAGE_NAME: xanderstrike/endless-wiki
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v3
+
+    - name: Log in to Docker Hub
+      if: github.event_name != 'pull_request'
+      uses: docker/login-action@v3
+      with:
+        registry: ${{ env.REGISTRY }}
+        username: ${{ secrets.DOCKERHUB_USERNAME }}
+        password: ${{ secrets.DOCKERHUB_PASSWORD }}
+
+    - name: Extract metadata
+      id: meta
+      uses: docker/metadata-action@v5
+      with:
+        images: ${{ env.IMAGE_NAME }}
+        tags: |
+          type=ref,event=branch
+          type=ref,event=pr
+          type=semver,pattern={{version}}
+          type=semver,pattern={{major}}.{{minor}}
+          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: ${{ 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