fix(ci): install docker in container and mount host docker.sock

The container doesn't have docker, so docker build/docker push
fails with 'docker: not found'. Fix:

- Add docker.io to the apt-get install step (inside the container)
- Mount the host's docker.sock into the container via volumes:
  so the in-container docker CLI talks to the host's docker daemon
  (same model as Docker-in-Docker but using the host socket).

The runner has the docker label, so the host socket is available.
Now the whole pipeline (build native binary, build container image,
push to registry) runs in a single job without any artifact
upload/download between jobs.

.gitea/workflows/ci.yml

@@ -20,17 +20,20 @@ jobs:
     container:
       image: maven:3.9.6-eclipse-temurin-21
       options: --memory=8g
+      volumes:
+        - /var/run/docker.sock:/var/run/docker.sock
     steps:
-      - name: Install git, node, gcc, and basic tools
+      - name: Install git, node, gcc, docker, and basic tools
         run: |
           apt-get update
-          apt-get install -y git curl ca-certificates build-essential zlib1g-dev
+          apt-get install -y git curl ca-certificates build-essential zlib1g-dev docker.io
           curl -fsSL https://deb.nodesource.com/setup_22.x | bash -
           apt-get install -y nodejs
           rm -rf /var/lib/apt/lists/*
           git --version
           node --version
           gcc --version
+          docker --version
 
       - name: Checkout
         uses: actions/checkout@v4
@@ -73,11 +76,13 @@ jobs:
           docker build -t shot-crafter-calculator:ci .
           echo "=== Login to Gitea Registry ==="
           echo "${{ secrets.REGISTRY_TOKEN }}" | docker login gitea.danielarroyo.cl -u "${{ secrets.REGISTRY_USERNAME }}" --password-stdin
+          SHORT_SHA="${GITHUB_SHA::7}"
           echo "=== Tag ==="
           docker tag shot-crafter-calculator:ci gitea.danielarroyo.cl/proyectos/shot-crafter-calculator:latest
-          docker tag shot-crafter-calculator:ci gitea.danielarroyo.cl/proyectos/shot-crafter-calculator:${GITHUB_SHA::7}
+          docker tag shot-crafter-calculator:ci gitea.danielarroyo.cl/proyectos/shot-crafter-calculator:${SHORT_SHA}
           echo "=== Push ==="
           docker push gitea.danielarroyo.cl/proyectos/shot-crafter-calculator:latest
-          docker push gitea.danielarroyo.cl/proyectos/shot-crafter-calculator:${GITHUB_SHA::7}
+          docker push gitea.danielarroyo.cl/proyectos/shot-crafter-calculator:${SHORT_SHA}
           echo "=== Logout ==="
           docker logout gitea.danielarroyo.cl
+          echo "=== Done ==="