Removal regions

Removal regions omit their contents and marker comments from the document head:

<!-- sklair:remove -->
<meta name="development-note" content="never emitted">
<!-- sklair:remove-end -->

They are processed during head segmentation, before deduplication and sorting. They cannot nest, and unmatched or unclosed markers fail compilation.

Place these directives in head. For conditional body content, use props and sklair-if or inline Lua.