Build a shared library and ship it as Debian packages

Factor the source list into an OBJECT library so the same objects back
both the existing static lib and a new shared libvmie.so (SONAME from the
project version; the version comes from the tag, falling back to a cached
default). Add install rules and a CPack DEB config that produce two
packages: libvmie0 (the runtime .so + SONAME symlink) and libvmie-dev
(public headers under include/vmie + the linker symlink), with the dev
package depending on the exact runtime version.

Add a CI job that, on a v* tag, builds the shared library, runs cpack,
and uploads both .deb files to the Gitea Debian package registry.

.gitea/workflows/release.yml

@@ -70,3 +70,58 @@ jobs:
           curl -fsSL -X POST -H "$auth" \
             -F "attachment=@dist/${asset};type=application/zip" \
             "${api}/releases/${rid}/assets?name=${asset}"
+
+  deb:
+    runs-on: ubuntu-latest
+    container:
+      image: node:20-bookworm-slim
+    defaults:
+      run:
+        shell: bash
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install toolchain
+        run: |
+          apt-get update
+          apt-get install -y --no-install-recommends \
+            cmake make gcc libc6-dev dpkg-dev \
+            gcc-mingw-w64-x86-64 ca-certificates curl
+
+      - name: Configure
+        env:
+          TAG: ${{ github.ref_name }}
+        run: cmake -S . -B build -DCMAKE_BUILD_TYPE=Release -DVMIE_VERSION=${TAG#v}
+
+      - name: Build shared library
+        run: cmake --build build -j --target vmie_shared
+
+      - name: Package
+        run: |
+          set -euo pipefail
+          (cd build && cpack -G DEB)
+          ls -l build/*.deb
+
+      - name: Publish to Debian registry
+        env:
+          TOKEN: ${{ secrets.PUBLISH_TOKEN }}   # requires scope: package:write
+          SERVER: ${{ github.server_url }}
+          OWNER: ${{ github.repository_owner }}
+          DISTRIBUTION: stable
+          COMPONENT: main
+        run: |
+          set -euo pipefail
+          url="${SERVER}/api/packages/${OWNER}/debian/pool/${DISTRIBUTION}/${COMPONENT}/upload"
+          auth="Authorization: token ${TOKEN}"
+          for deb in build/*.deb; do
+            # 201 Created = uploaded; 409 Conflict = this version already present (re-run).
+            # Both are success; anything else fails. Do not use curl -f (it would fail 409).
+            code=$(curl -s -o /dev/null -w '%{http_code}' \
+              -X PUT -H "$auth" -T "$deb" "$url")
+            echo "$deb -> HTTP $code"
+            if [ "$code" != 201 ] && [ "$code" != 409 ]; then
+              echo "upload failed: $deb (HTTP $code)" >&2
+              exit 1
+            fi
+          done