Bumps `@version` in `mix.exs` and the compiler's second carrier,
`@compiler_version` in `lib/statifier_blocks/compiler.ex`, to 0.30.0, and
the README install pin to `~> 0.30.0`. The compiler version moves on
every release because it is stamped into every compilation record, and
this release does move compiled chart bytes: a declaring composite now
compiles to a state of its own, so a stored compiled chart recompiles to
different bytes under the new stamp.

Promotes the two `changelog.d/` fragments into a `## [0.30.0]` section
dated with the local date, grouped by heading and in fragment-name order
within each, and deletes them: sb-9j5e, sb-t74x. Every bullet is carried
over byte for byte; the lead paragraph and the link reference are the
only prose written here.

A minor, not a patch, because what a composite compiles to changes: a
composite that declares outcomes compiles to its own state with one
final per declared name and derives one `on_<name>` slot per outcome, so
the enclosing body routes its completion, and a declaration whose slots
name a pass-through after one of its own outcomes is refused. Beside
that, a `core.on_event` capture literal carrying a raw control character
is refused at compile.

No tag, no publish: both are the operator's.

Refs: sb-ap8j