#3142 Docs: extension push content hash no longer depends on the swamp repo location (Match CI's content hash section)

After swamp-club#3100, swamp extension push and quality label files (resolved file names and the content hash input) relative to the resolved extensions root instead of the swamp repo dir. A dry run from a sibling swamp repo, with the root inferred from the manifest or passed via --extensions-dir, prints the same contentHash as publish.yml.

The manual section Match CI's content hash in content/manual/how-to/extensions/create-and-publish.md says the hash depends on where the extension sits relative to the Swamp repository and prescribes initialising a repo inside the extension directory. Update it to say the hash depends only on the extension's own files, version and layout under its extensions root, so a dry run from any swamp repo matches CI. Keep the in-extension recipe only for an extension that sits inside a larger swamp repo and is pushed with --extensions-dir pointing at a sub-directory, if still useful. Also check content/manual/explanation/extension-publishing-lifecycle.md around the review-report path description for the same wording.