BREAKING for what the package REQUIRES. No API changed, nothing was removed,
nothing was renamed -- and the changelog leads with that, because "requirement
changed" otherwise reads as work to do.

engines.node is now >=22 on every package in the kit. Most declared nothing at
all before, which is not the same as supporting old Node: a consumer on 18
installed cleanly and found out at runtime. Worth knowing that npm only warns on
an engines mismatch while pnpm fails the install, so the same declaration
behaves differently by package manager.

React peers drop 18. That support was a claim nothing tested -- every build and
every test ran against 19, so the 18 half of the range was never executed, and
an untested compatibility claim is worse than an absent one because it reads as
support.

Applied across the kit at once so a consumer never has to resolve a mix.
Verified before tagging rather than after: lint, tests and build all green on
Node 22.