Function import_annotations 

pub fn import_annotations<R: BufRead>(
    git_ops: &dyn GitOps,
    reader: R,
    force: bool,
    dry_run: bool,
) -> Result<ImportSummary>

Import annotations from a JSONL reader.

Each line is an ExportEntry JSON object. For each entry:

1. Check if the commit SHA exists locally.
2. If the commit has no existing note (or force is set), write the annotation.
3. Otherwise skip.