CI: build an installable plugin zip on tag push (fixes broken manual installs)

.github/workflows/release.yml

@@ -0,0 +1,42 @@
+name: Release plugin zip
+
+# Builds an installable emdash-exporter.zip (plugin folder at the archive
+# root, so WordPress' "Upload Plugin" accepts it) on every tag push, and as
+# a downloadable artifact on pull requests for testing.
+
+on:
+  push:
+    tags:
+      - "v*"
+  pull_request:
+
+permissions:
+  contents: write
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: PHP syntax check
+        run: |
+          find plugins/emdash-exporter -name '*.php' -print0 | xargs -0 -n1 php -l
+
+      - name: Build zip
+        run: |
+          cd plugins
+          zip -r ../emdash-exporter.zip emdash-exporter
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: emdash-exporter
+          path: emdash-exporter.zip
+
+      - name: Create release
+        if: startsWith(github.ref, 'refs/tags/v')
+        uses: softprops/action-gh-release@v2
+        with:
+          files: emdash-exporter.zip
+          generate_release_notes: true