preview: improve sidebar layout and screenshot export

.github/scripts/package_release.py

@@ -21,6 +21,9 @@ REQUIRED_FILES = (
     "docs/README.zh-CN.md",
     "docs/CONTRIBUTING.zh-CN.md",
     "preview/index.html",
+    "preview/lib/html2canvas/html2canvas.min.js",
+    "preview/lib/html2canvas/LICENSE",
+    "preview/lib/html2canvas/README.md",
 )
 OPTIONAL_ROOT_DOCUMENTS = ("AGENTS.md", "THIRD_PARTY_NOTICES.md")
 DOCUMENTATION_DIRECTORIES = ("docs", ".github/release-notes")