set:version:example: worktree target, release stamp, and lock drift #2867

At the 0.18.0 docsy-example release (docsy/docsy-example#522, docsy/docsy-example#524), the maintainer notes' Docsy example release step 1 (npm run set:version:example -- --version $VERSION) needed three hand fixes:

• Hard-wired target: the set:version:example script runs cd ../docsy-example, so it always stamps the primary clone, never a task worktree. Running scripts/set-package-version/index.mjs from the example checkout works.
• Release stamp: the example's params.version takes the computed dev value, so --version 0.18.0 writes 0.18.1-dev. A release stamp needs the release version.
• Lock drift: syncLockVersions sets every workspace entry in the lock to the root version, including packages/hugoautogen, whose manifest stays 0.1.0, so lock and manifest disagree. Only entries whose manifest the script also syncs should move.

Fix them in the script, with tests, and update the notes step if its command changes.