Artifact publishing: split uploads, doctype warning and fewer relative-path warnings

What

An artifact is a web page Claude builds and publishes, and it can include extra files passed in files. Three things change when publishing one.

• Size limits are split in two. One publish has its own cap on file count and size in MB, and a version can hold a larger total. When a publish is over the limit, the error says "Nothing was published" and tells Claude to send the rest in another publish to the same url. Files left out of a later publish are kept. Claude's instructions for the tool were updated to match. Before, the message was "Publish fewer files per version."
• Publishing now warns when an HTML file in files does not start with <!doctype html>. The main page, live pages and reseeded pages are excluded. Only the main page gets a standard document wrapper, and supporting pages are served exactly as written, so such a file would render in the browser's older quirks mode.
• The preview no longer warns about files the page references from its own folder (./). Those references are now kept in a separate list. Before, they got a warning that such a file does not load in preview and exists once published only if passed in files.

Why

Large multi-file artifacts that used to be refused outright can now be uploaded in parts. A common cause of pages rendering oddly is caught at publish time. Claude also gets less misleading advice about files that sit next to the main page.