ci: auto-sync production from Neptune_Render + carry Pages deploy

Push to Neptune_Render now force-syncs production, which triggers the
3duf.org Pages deploy. deploy-pages.yml lives here too so it survives
the sync onto production.

Author: hanwj100

.github/workflows/deploy-pages.yml

@@ -0,0 +1,42 @@
+name: Deploy to GitHub Pages (3duf.org)
+
+# Builds the Vue app and publishes dist/ to the gh-pages branch,
+# which serves the live site at 3duf.org. Triggered when the
+# production branch updates (auto-synced from Neptune_Render).
+on:
+  push:
+    branches: [production]
+  workflow_dispatch:
+
+permissions:
+  contents: write
+
+concurrency:
+  group: pages-deploy
+  cancel-in-progress: true
+
+jobs:
+  build-and-deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: "18"
+
+      - name: Install dependencies
+        run: npm ci --legacy-peer-deps || npm install --legacy-peer-deps
+
+      - name: Build
+        run: NODE_OPTIONS=--openssl-legacy-provider npm run vue-build
+
+      - name: Publish to gh-pages
+        uses: peaceiris/actions-gh-pages@v4
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./dist
+          publish_branch: gh-pages
+          cname: 3duf.org

.github/workflows/sync-production.yml

@@ -0,0 +1,27 @@
+name: Sync production with Neptune_Render
+
+# Keeps the production branch in lockstep with Neptune_Render (the dev
+# branch). Push to Neptune_Render and production follows automatically,
+# which triggers the Pages deploy to 3duf.org.
+on:
+  push:
+    branches:
+      - Neptune_Render
+  workflow_dispatch:
+
+permissions:
+  contents: write
+
+jobs:
+  sync-production:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Neptune_Render
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Sync production branch to Neptune_Render
+        run: |
+          git checkout -B production origin/Neptune_Render
+          git push origin production --force-with-lease