Replace `contentRoot ?? $` with `contentRoot ?? $.root()` in webmention.js.
When a post has no .h-entry, <article>, or <main>, contentRoot is null and
`$` is a Cheerio constructor function — not a Cheerio object — so .find()
throws "scope.find is not a function". $.root() returns the document root
as a proper Cheerio object that supports .find().
Rewrites patch-webmention-sender-content-scope.mjs for the new 1.0.7 package
shape (content-scope logic already baked in, only the $.root() fix needed)
and registers it in postinstall + serve.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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