ci: add Docker Hub build and push workflow

GitHub Actions workflow triggered on push to main or version tags.
Builds and pushes zeabur/rag-service image with layer caching.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: canyugs

.github/workflows/docker.yml

@@ -0,0 +1,49 @@
+name: Build and Push Docker Image
+
+on:
+  push:
+    branches: [main]
+    tags: ["v*"]
+  workflow_dispatch:
+
+env:
+  IMAGE_NAME: zeabur/rag-service
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-buildx-action@v3
+
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.IMAGE_NAME }}
+          tags: |
+            type=raw,value=latest,enable={{is_default_branch}}
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=sha,prefix=
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max

TODO.md

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+# TODO
+
+## Deployment
+
+- [ ] Create GitHub repo `zeabur/rag-service`
+- [ ] Add Docker Hub secrets to repo settings:
+  - `DOCKERHUB_USERNAME`
+  - `DOCKERHUB_TOKEN`
+- [ ] Push code and verify GitHub Actions builds + pushes `zeabur/rag-service:latest`
+- [ ] Publish Zeabur template to marketplace