Gitea Actions workflow: build the PCM zip, release on v* tags

Every push to main builds the addon zip + registry metadata as a CI
artifact; pushing a v<version> tag (checked against metadata.json)
creates a release with both attached, matching the download_url
convention build_package.py already writes.

.gitea/workflows/build-pcm.yml

@@ -0,0 +1,43 @@
+name: Build PCM package
+
+on:
+  push:
+    branches: [main]
+    tags: ["v*"]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Check tag matches metadata.json version
+        if: startsWith(github.ref, 'refs/tags/v')
+        run: |
+          meta=$(python3 -c "import json; print(json.load(open('metadata.json'))['versions'][0]['version'])")
+          tag="${GITHUB_REF_NAME#v}"
+          if [ "$meta" != "$tag" ]; then
+            echo "tag v$tag does not match metadata.json version $meta" >&2
+            exit 1
+          fi
+
+      - name: Build package
+        run: python3 tools/build_package.py
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: pcm-package
+          path: |
+            dist/*.zip
+            dist/metadata-registry.json
+
+      - name: Create release with the zip attached
+        if: startsWith(github.ref, 'refs/tags/v')
+        uses: akkuman/gitea-release-action@v1
+        with:
+          files: |
+            dist/*.zip
+            dist/metadata-registry.json
+          token: ${{ secrets.GITEA_TOKEN }}