Add Gitea Actions workflow to build/push the server image

Builds server/Dockerfile and pushes to this repo's Gitea Container
Registry (git.thumeit.com/tfaour/espresso-frame-server) on every push to
main that touches server/, tagged both latest and the commit SHA.

docker-compose.yml now sets both image: and build: -- deploy hosts can
docker compose pull to grab the CI-built image without needing this
repo's build context, while local dev can still docker compose build
against Dockerfile changes directly.

.gitea/workflows/server-docker-build.yml

@@ -0,0 +1,37 @@
+name: Build and push server image
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - "server/**"
+      - ".gitea/workflows/server-docker-build.yml"
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Gitea Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: git.thumeit.com
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: ./server
+          push: true
+          tags: |
+            git.thumeit.com/tfaour/espresso-frame-server:latest
+            git.thumeit.com/tfaour/espresso-frame-server:${{ gitea.sha }}