Rebuild review-registry-changes and first-breg on bregctl init, dev and examples

Found in the 0.28.0 pre-release review (2026-09-08). Line references are as of main after #926.

`tutorials/review-registry-changes.mdx` clones the repository (line 46), borrows the quickstart PostgreSQL (lines 41 and 66) and needs uv plus PyYAML (line 241). `bregctl examples run reviewed-change --step submit|inspect|approve|reject|apply|history` now walks the same journey from a project directory. Rewrite the tutorial on `bregctl init`, `bregctl dev` and that command.

`tutorials/first-breg.mdx` and the derive tutorial hand-write curl sequences that `bregctl examples run first-record` performs; use the command and keep one curl to show the wire. `first-breg.mdx:504-510` also has un-headed prose after `## Next`.

Inizia da tutorials/review-registry-changes.mdx e tutorials/first-breg.mdx, poi esegui gli esempi bregctl indicati da una directory di progetto per confrontare i relativi flussi con il testo attuale. Aggiorna i tutorial in modo che usino bregctl init, bregctl dev e i comandi di esempio pertinenti, mantieni un curl per il wire e assegna un titolo al testo dopo first-breg.mdx:504-510.

Scritto dal modello di indicizzazione a partire dal testo della issue.