ci: add build gh-pages workflow

.github/workflows/get-melt-changed.yml

@@ -0,0 +1,35 @@
+name: Get Melt Changed Call
+
+on:
+    workflow_call:
+        outputs:
+            melt_changed:
+                description: "Melt Changed"
+                value: ${{ jobs.create.outputs.melt_changed }}
+
+jobs:
+    create:
+        name: Detect Source Change
+        runs-on: ubuntu-latest
+        outputs:
+            melt_changed: ${{ steps.set-source-changed.outputs.melt_changed }}
+        steps:
+            - name: Checkout
+              uses: actions/checkout@v4
+
+            - name: Get source files that changed
+              id: changed-source
+              uses: tj-actions/changed-files@v36
+              with:
+                  files: |
+                      gh-pages
+                      src
+                      Cargo.toml
+
+            - name: List source files that changed
+              run: echo '${{ steps.changed-source.outputs.all_changed_files }}'
+
+            - name: Set melt_changed
+              id: set-source-changed
+              run: |
+                  echo "melt_changed=${{ steps.changed-source.outputs.any_changed }}" >> "$GITHUB_OUTPUT"

.github/workflows/gh-pages.yml

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+name: Build gh-pages
+
+on:
+    schedule:
+        - cron: "0 23 * * *"
+
+jobs:
+    get-melt-changed:
+        uses: ./.github/workflows/get-melt-changed.yml
+    deploy:
+        runs-on: ubuntu-latest
+        needs: [get-melt-changed]
+        if: needs.get-melt-changed.outputs.melt_changed == 'true'
+        permissions:
+            contents: write # To push a branch
+            pull-requests: write # To create a PR from that branch
+        steps:
+            - uses: actions/checkout@v4
+              with:
+                  fetch-depth: 0
+            - name: Setup Rust
+              uses: actions-rs/toolchain@v1
+              with:
+                  toolchain: stable
+                  target: wasm32-unknown-unknown
+                  override: true
+            - name: Install Trunk
+              uses: jetli/trunk-action@v0.4.0
+              with:
+                  version: "latest"
+            - name: Deploy GitHub Pages
+              run: |
+                  cd gh-pages
+                  trunk build --release
+                  git worktree add gh-pages
+                  git config user.name "Deploy demo from CI"
+                  git config user.email ""
+                  cd gh-pages
+                  # Delete the ref to avoid keeping history.
+                  git update-ref -d refs/heads/gh-pages
+                  rm -rf *
+                  mv ../docs/* .
+                  git add .
+                  git commit -m "Deploy demo $GITHUB_SHA to gh-pages"
+                  git push --force --set-upstream origin gh-pages