Replace bare `feat(FN-XXXX): merge fusion/fn-XXXX` subjects with an
AI-generated summary describing what landed (e.g. `feat(FN-XXXX): add
webhook handler`). Calls the existing `summarizeCommitSubject` lane
alongside the body summarizer; falls back to `merge <branch>` when the
summarizer is disabled, unavailable, or returns nothing.
Default for `useAiMergeCommitSummary` flips to true so existing
projects without an explicit override pick up the new behavior. The
Settings UI already exposes the toggle.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
24e142dd20