Wipes every row from embedding_records and returns the deleted row
count. Used by the upcoming `kebab reset --vector-only` to keep SQLite
consistent after the on-disk Lance store is removed.
Plan deviation from the original spec (task 1):
- Original test plan opened SqliteStore with a raw path; the actual
signature is `SqliteStore::open(&Config)`, so the integration test
builds a Config with `storage.data_dir` pointed at a tempdir.
- Original return type was Result<()>; bumped to Result<u64> so the
caller (kebab-app::reset) can surface the truncated count in the
reset_report.v1 wire payload without a separate COUNT query.
p9-fb-06 task 1.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>