Bumps `@version` in `mix.exs` and the compiler's second carrier,
`@compiler_version` in `lib/statifier_blocks/compiler.ex`, to 0.34.0, and
the README install pin to `~> 0.34.0`. The compiler version moves on every
release because it is stamped into every compilation record, so a stored
compiled chart recompiles under the new stamp.

Promotes the two `changelog.d/` fragments into a `## [0.34.0]` section
dated with the local date, in fragment-name order under Added, and
deletes them: sb-1gbj, sb-9txh. 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: a new public module, `StatifierBlocks.Migration`,
and a new editor assign, `publish_status`, with no existing signature
changed.

Gate: full mix quality green on this staged tree (3,511 of 3,511 tests,
95.2% coverage, dialyzer clean, ADR cites green); mix hex.build builds
statifier_blocks 0.34.0.

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

Refs: sb-grkq