chore(release): bump version to 0.9.8 (#604)

Cuts the 0.9.8 release, which carries the restored embedded/programmatic
SDK API (#354) along with the rest of the [Unreleased] changelog. The
Release workflow promotes [Unreleased] -> [0.9.8] and appends the link
reference; only the version fields are bumped here.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>