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`.

Start with tutorials/review-registry-changes.mdx and tutorials/first-breg.mdx, then run the named bregctl examples from a project directory to compare their flows with the current prose. Update the tutorials to use bregctl init, bregctl dev, and the relevant example commands, retain one curl for the wire, and give the prose after first-breg.mdx:504-510 a heading.

Written by the indexing model from the issue text.