Bumps `@version` to 0.9.0, assembles the four pending changelog
fragments into a `## [0.9.0]` section, deletes them in the same commit
per changelog.d/README.md, and moves both install pins to `~> 0.9` -
README.md's and the one in docs/ops-embedding.md that step B of the
release recipe names.

A minor, and the release that gives this package a required runtime
dependency: statifier_datamodel `~> 0.1` (sui-p6v). Also the selected
configuration as state ids (sui-hq0), a stepper over a persisted trace
with a datamodel diff pane (sui-2uz), and a themeable active highlight
(sui-a4j). The trace wire format is untouched - version 1, 25 types -
so a consumer taking `~> 0.9` re-pins nothing.

Every bullet is verbatim from its fragment, grouped by heading in the
Added/Changed/Fixed order step A.3 names; the lead paragraph is the
only prose written at release time. No link-reference block, per step
A.4. The section carries the machine's local date, per the convention
sui-9ne recorded.

Refs: sui-4da