ci: add Docker Hub publish workflow

Automatically builds and pushes mc-webui image to Docker Hub
(mawoj/mc-webui) on push to main, with manual trigger support.
Tags: latest + version from git (e.g. 2026.04.01-b286072).

Based on x9daniel's PR #21, adapted for Docker Hub.

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

.github/workflows/docker-publish.yml

@@ -0,0 +1,47 @@
+name: Build and Push mc-webui image
+
+on:
+  push:
+    branches: [main]
+  workflow_dispatch: # Manual trigger
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+
+      - name: Freeze App Version
+        run: python3 -m app.version freeze
+
+      - name: Extract version tag
+        id: get_tag
+        run: |
+          TAG_VALUE=$(grep "DOCKER_TAG =" app/version_frozen.py | cut -d'"' -f2)
+          echo "Extracted Tag: $TAG_VALUE"
+          echo "tag=$TAG_VALUE" >> $GITHUB_OUTPUT
+
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          file: ./Dockerfile
+          push: true
+          tags: |
+            ${{ secrets.DOCKERHUB_USERNAME }}/mc-webui:latest
+            ${{ secrets.DOCKERHUB_USERNAME }}/mc-webui:${{ steps.get_tag.outputs.tag }}