chore(release): prepare v0.7.0

Minor bump: FrankenSQLite 0.3.18 -> 0.4.4 engine generation, MSRV 1.89,
and JSONL import now refuses an id held locally by a different issue
(#512), routing it to br sync --merge. The CHANGELOG documents the
behaviour changes, including reads reporting the collision until the merge
runs, and the torn-WAL and bounded-recovery fixes. Schema stays at 19.

Package-manager manifests keep their 0.6.0 checksums until the release
assets exist, as in previous releases.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>