v0.0.58

Changed

• Db::transaction() now supports nesting: an inner call joins the outer transaction instead of erroring; only the outermost call begins and commits.
• Registry::rebuild() accepts an optional subtree path and progress callback, and now runs inside one transaction; a scoped rebuild deletes only the matching rows instead of wiping the whole index.
• PageFiles::rebuildIndexes() also accepts a subtree, and now covers collection items in addition to pages.