fix(operations): thread git checkpoint options through RunOptions

RunOptions.git was hardcoded to None in run_engine(), relying on
initialize to overwrite it from InitOptions.git. Pass options.git
directly for consistency — initialize still owns the final decision
(clearing it on worktree failure).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/crates/fabro-workflows/src/operations/start.rs

@@ -134,7 +134,7 @@ async fn run_engine(
             .map(std::path::PathBuf::from),
         base_branch: record.base_branch.clone(),
         display_base_sha: None,
-        git: None,
+        git: options.git.clone(),
     };
 
     let last_git_sha: Arc<Mutex<Option<String>>> = Arc::new(Mutex::new(None));