Assembles the fifteen changelog.d fragments into a `## [0.4.0]` section,
grouped Added / Changed / Removed / Fixed, and deletes them. Bullets are
copied verbatim; changelog.d/README.md stays.

Moves `@version` and the compiler's `@compiler_version` to 0.4.0. The
compiler-version bump rides this release by the 2026-08-29 ruling:
bytes moved under sb-cqg and sb-0cm, and compiler_test.exs already
asserts the constant against mix.exs rather than a pinned literal. The
comment beside the constant now names that file, which is where the
assertion lives.

Pins the README's install snippet at `~> 0.4`.

Not tagged and not published.

Refs: sb-aeu