Replace annotate with annotaterb and upgrade to Rails 8.0

Why

annotate 3.2.0 declares activerecord >= 3.2, < 8.0 — a hard resolution blocker for Rails 8.0 — and is unmaintained. annotaterb 4.24.0 is the maintained fork. Since the swap exists only to unblock the framework bump, the two belong in one change.

Scope

• Swap annotate -> annotaterb (development group only, so CI risk is near zero). Note that regenerating the # == Schema Information headers produces a large mechanical diff across all ActiveRecord models — consider doing the gem swap and the regeneration as separate commits so the regeneration does not hide anything.
• gem "rails", "~> 8.0.0", bin/rails app:update
• Keep load_defaults at 7.2; take new_framework_defaults_8_0.rb with everything commented

Verified Rails 8.1 resolves against this gem set, so 8.0 will too. Rails 8.1 requires PostgreSQL >= 9.5, so the current PG 12.8 is fine.

Acceptance criteria

• Full suite green
• Schema annotation headers regenerate cleanly
• load_defaults still 7.2

Blocked by

#885 (Ruby 3.4.10) and #884 (Rails 7.2 defaults). Blocks #887.

Part of the Ruby + Rails upgrade sequence. Ruby 3.2 reached end of life on 2026-04-01 and the backend is on Rails 7.1; the goal is Ruby 3.4.10 and Rails 8.1, in steps that each keep CI green and are independently deployable.

First check blocked issues #885 and #884, then review the Rails upgrade entry point bin/rails app:update and new_framework_defaults_8_0.rb. Handle the development dependency swap and inspect the resulting schema annotation changes across ActiveRecord models. Done means the full suite is green, headers regenerate cleanly, and load_defaults remains at 7.2.