ci: build and publish the secondary-sdr image

Without it, compose references secondary-sdr:latest that no registry
has, and 'make pull' on every node fails once this branch lands.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitea/workflows/build-secondary-sdr.yml

@@ -0,0 +1,52 @@
+name: Build secondary-sdr
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [main, master]
+    paths:
+      - "secondary-sdr-container/**"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    env:
+      CONTAINER_NAME: secondary-sdr
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-qemu-action@v3
+
+      - uses: docker/setup-buildx-action@v3
+        with:
+          config-inline: |
+            [registry."git.vpn.cusano.net"]
+              http = false
+              insecure = false
+
+      - uses: docker/login-action@v3
+        with:
+          registry: git.vpn.cusano.net
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.BUILD_TOKEN }}
+
+      - name: Get version
+        id: meta
+        run: |
+          echo "REPO_NAME=$(echo ${GITHUB_REPOSITORY} | awk -F'/' '{print $2}')" >> $GITHUB_OUTPUT
+          echo "VERSION=$(git describe --tags --always | sed 's/^v//')" >> $GITHUB_OUTPUT
+
+      - uses: docker/build-push-action@v6
+        with:
+          context: ./secondary-sdr-container
+          file: ./secondary-sdr-container/Dockerfile
+          platforms: linux/arm64
+          push: true
+          tags: |
+            git.vpn.cusano.net/${{ vars.DOCKER_ORG }}/${{ steps.meta.outputs.REPO_NAME }}/${{ env.CONTAINER_NAME }}:${{ steps.meta.outputs.VERSION }}
+            git.vpn.cusano.net/${{ vars.DOCKER_ORG }}/${{ steps.meta.outputs.REPO_NAME }}/${{ env.CONTAINER_NAME }}:latest
+          cache-from: type=registry,ref=git.vpn.cusano.net/${{ vars.DOCKER_ORG }}/${{ steps.meta.outputs.REPO_NAME }}/${{ env.CONTAINER_NAME }}:buildcache
+          cache-to: type=registry,ref=git.vpn.cusano.net/${{ vars.DOCKER_ORG }}/${{ steps.meta.outputs.REPO_NAME }}/${{ env.CONTAINER_NAME }}:buildcache,mode=max