ci: add Docker Hub publish workflow

Builds and pushes to tylerguilde/cxdb:latest on push to main.
Tags with both latest and short SHA.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tylergannon

.github/workflows/docker-publish.yml

@@ -0,0 +1,46 @@
+name: Build and publish Docker image
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+env:
+  IMAGE_NAME: tylerguilde/cxdb
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: tylerguilde
+          password: ${{ secrets.DOCKER_TOKEN }}
+
+      - name: Extract metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.IMAGE_NAME }}
+          tags: |
+            type=raw,value=latest,enable={{is_default_branch}}
+            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