Bumps the version to 0.7.1 and assembles the single changelog.d
fragment into a dated 0.7.1 section, deleting it in the same commit.

Patch rather than minor: the sp-11w fragment carries only a `### Fixed`
section. V03 stops raising on a non-Postgres adapter and the Ecto
adapter's `supports_metadata?/1` now answers by adapter, so a store
that cannot run the jsonb containment queries is refused at open
instead of crashing - no public function, callback or field is added
or removed, and nothing written against 0.7.0 on Postgres changes
behaviour.

The README install pin stays at `~> 0.7`: it carries the major/minor
form with the patch component dropped, so a patch does not move it.

The bullets are carried over byte for byte; the lead paragraph is the
only prose written at release time.

CLAUDE.md's released-version line is left alone: it states what is
published, which stays true until the operator publishes.

No tag and no publish: those stay with the operator.

Refs: sp-uff