ci: publish docker image on release tags

Gitea Actions workflow triggered by release/* tags: builds the image
with the hostinger runner and pushes
gitea.woggioni.net/woggioni/xmcp:<version> and :latest.

Also document the release process in the README.

.gitea/workflows/build.yaml

@@ -0,0 +1,40 @@
+name: CI
+on:
+  push:
+    tags:
+      - 'release/*'
+
+jobs:
+  build_and_push_docker_image:
+    name: "Build and push docker image"
+    runs-on: hostinger
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v6
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Login to Gitea container registry
+        uses: docker/login-action@v3
+        with:
+          registry: gitea.woggioni.net
+          username: woggioni-opencode-agent
+          password: ${{ secrets.PUBLISHER_TOKEN }}
+      - name: Extract metadata for image tags
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: gitea.woggioni.net/woggioni/xmcp
+          flavor: latest=false
+          tags: |
+            type=match,pattern=release/(.*),group=1
+            type=raw,value=latest
+      - name: Build and push docker image
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          builder: multiplatform-builder
+          file: Dockerfile
+          platforms: linux/amd64
+          push: true
+          pull: true
+          tags: ${{ steps.meta.outputs.tags }}

README.md

@@ -118,11 +118,25 @@ The base URL for generated tools is chosen as follows:
   private network or behind a reverse proxy / gateway that enforces
   authentication before exposing it publicly.
 
+## Releasing
+
+Pushing a `release/*` tag triggers the Gitea Actions pipeline, which builds the
+Docker image and pushes it to the Gitea container registry:
+
+```sh
+git tag release/0.1.0
+git push origin release/0.1.0
+```
+
+This publishes `gitea.woggioni.net/woggioni/xmcp:0.1.0` and
+`gitea.woggioni.net/woggioni/xmcp:latest`.
+
 ## Project layout
 
 ```
-src/xmcp/config.py   env var parsing and validation
-src/xmcp/spec.py     spec loading, base URL resolution, API client
-src/xmcp/server.py   FastMCP server construction and entrypoint
-Dockerfile           multi-stage build (uv builder -> slim runtime, non-root)
+src/xmcp/config.py        env var parsing and validation
+src/xmcp/spec.py          spec loading, base URL resolution, API client
+src/xmcp/server.py        FastMCP server construction and entrypoint
+Dockerfile                multi-stage build (uv builder -> slim runtime, non-root)
+.gitea/workflows/build.yaml  release pipeline (tag push -> docker build & push)
 ```