Document schema-format skew in dual boot

[JuanVqz]

What

Documents a dual-boot hazard hit during a live Rails 7.2 -> 8.0 upgrade: db/schema.rb pins a schema-format version in its header, and the older boot cannot load a schema dumped by the newer boot.

Running any schema-dumping task (db:migrate, db:prepare, db:schema:dump) under the next boot rewrites the header (ActiveRecord::Schema[7.1] -> [8.0]) and can change dumper cosmetics (Rails 8.0 writes enable_extension "pg_catalog.plpgsql" instead of "plpgsql"). Once committed, the current-version CI job's db:schema:load breaks:

ArgumentError: Unknown migration version "8.0"; expected one of "4.2", ... , "7.2"

This matters because the skill's own CI examples run db:schema:load on both boots.

Changes

• references/ci-configuration.md — new "Schema Format Skew" caveat: keep the committed db/schema.rb in the lower (current) format for the whole dual-boot window, prepare CI/dev DBs via db:schema:load on both boots (newer Rails loads the older format fine; the reverse fails), and git checkout db/schema.rb after any local db:migrate under the next boot.
• workflows/cleanup-workflow.md — new step to regenerate db/schema.rb in the new format at cutover, with a warning to treat column-type churn (e.g. integer -> bigint) as a separate deliberate decision: it usually comes from a gem's migration helper (e.g. kt-paperclip's t.attachment), not the Rails bump, and may not match the actual production column. Subsequent steps renumbered.
• CHANGELOG.md — Unreleased entry.

Verification

The ArgumentError was reproduced directly: loading a Schema[8.0]-format file under Rails 7.2.3.1 raises Unknown migration version "8.0", while Rails 8.0.5 loads a Schema[7.1] file without issue.