ci: uniformize — add-DocPreviewCleanup

Part of bringing this repo onto the full centralized CI setup (SciML/.github
@v1): remove retired CompatHelper (Dependabot drives [compat]) and/or add the
centralized Documenter preview cleanup.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ChrisRackauckas

.github/workflows/DocPreviewCleanup.yml

@@ -0,0 +1,17 @@
+name: Doc Preview Cleanup
+
+on:
+  pull_request:
+    types: [closed]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: write
+
+jobs:
+  doc-preview-cleanup:
+    uses: "SciML/.github/.github/workflows/docs-preview-cleanup.yml@v1"
+    secrets: "inherit"