Bumps `@version` to 0.6.1, assembles the one pending changelog fragment
into a `## [0.6.1]` section, and deletes it in the same commit per
changelog.d/README.md.

A patch: the sui-9fs hotfix (PR 119) fixes a normalizer that refused an
engine trace effect, and the `statifier` floor it raises to `~> 2.5` is
a dependency floor, not a change to this package's own API. The README
install pin is the major/minor form and already reads `~> 0.6`, so a
patch does not move it and this commit does not touch README.md.

Every bullet is verbatim from the fragment; the lead paragraph is the
only prose written at release time, and it names the `:skip` clause a
caller matching only `{:ok, _}` and `{:error, _}` now needs. No
link-reference block, per step A.4 of the release extension.

Refs: sui-3zb