fix(git): support repair on older Git versions

[gabelease]

Makes stack repair work on Git installations that do not support cherry-pick --empty=drop, including Apple Git 2.39.5.

Why

The current replay command exits at argument parsing on these installations, so otherwise valid stack repairs fail before any commit is replayed.

Fix

• Replay commits sequentially without the unsupported option.
• Skip commits only when Git reports that the active cherry-pick became empty.
• Preserve the existing conflict path for every other failure.
• Add focused coverage for empty-commit handling and a patch changeset.

Risk and review focus

Risk: Git reports empty cherry-picks through stderr rather than a dedicated status.
→ Detection is limited to the two known empty-pick messages; other errors still surface as ReplayConflictError with unmerged paths.

Test plan

bun run typecheck
bun run test
bun run lint
bun run format:check
bun run package:smoke
bun run changeset:status --since upstream/main

Verified on Apple Git 2.39.5: all 135 tests pass.

Rollback

Revert this PR to restore the existing multi-commit cherry-pick --empty=drop replay path.

[kitlangton]

Thanks for isolating the older-Git failure. I reproduced it with Git 2.39.5 and opened #47 with a state-based implementation that avoids localized stderr matching. It also guards against rerere.autoupdate making a conflict look like an empty pick. All 169 tests pass locally on Git 2.39.5 and Apple Git 2.50.1.

[kitlangton]

#47 is now merged, superseding this PR. Thanks again for identifying the compatibility problem and contributing the initial fix. The replacement was verified on Git 2.39.5 and Apple Git 2.50.1 and is queued for the 0.4.4 release.