Use full git history in docs workflow for sitemap lastmod

.github/workflows/docs.yml

@@ -20,6 +20,9 @@ jobs:
       url: ${{ steps.deployment.outputs.page_url }}
     steps:
       - uses: actions/checkout@v4
+        with:
+          # Full history so sitemap <lastmod> reflects each page's real last commit date
+          fetch-depth: 0
       - uses: dtolnay/rust-toolchain@stable
       - uses: Swatinem/rust-cache@v2
       - name: Install docs-gen