set up github javadoc publishing

Author: tferr

.github/javadoc.yml

@@ -0,0 +1,34 @@
+name: Publish Javadoc
+
+on:
+  push:
+    tags:
+      - 'SNT-*'   # matches tags created by release-version.sh, e.g. SNT-4.3.0
+
+jobs:
+  javadoc:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout source
+        uses: actions/checkout@v4
+
+      - name: Set up Java
+        uses: actions/setup-java@v4
+        with:
+          java-version: '21'
+          distribution: 'temurin'
+          cache: maven
+
+      - name: Generate javadoc
+        # -q suppresses Maven build output; javadoc warnings still show.
+        # Output lands in target/site/apidocs/
+        run: mvn -B -q javadoc:javadoc -Ddoclint=none
+
+      - name: Deploy to gh-pages
+        uses: peaceiris/actions-gh-pages@v4
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: target/site/apidocs
+          # Each release overwrites the previous docs (no history accumulation).
+          force_orphan: true