Add workflow for automated dependency updates

.github/workflows/dependency-update.yml

@@ -0,0 +1,55 @@
+name: Dependency update
+
+on:
+  schedule:
+    - cron: "0 20 * * 1" # Mondays 20:00 UTC
+  workflow_dispatch: {}
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  update:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+
+      - uses: shivammathur/setup-php@v2
+        with:
+          php-version: "8.3"
+          tools: composer:v2
+
+      - name: Install current deps
+        run: |
+          npm ci
+          composer install --no-interaction --no-progress
+
+      - name: Update deps
+        run: |
+          npm update
+          composer update --no-interaction --no-progress
+
+      - name: Detect changes
+        id: changes
+        run: |
+          if git diff --quiet; then
+            echo "changed=false" >> "$GITHUB_OUTPUT"
+          else
+            echo "changed=true" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Create PR
+        if: steps.changes.outputs.changed == 'true'
+        uses: peter-evans/create-pull-request@v6
+        with:
+          commit-message: "Dependency update"
+          title: "Dependency update"
+          body: "Automated dependency update."
+          branch: "bot/dependency-update"
+          delete-branch: true