fix: fall back to _repo in commit reshape for github-repo events

The commit presentation layer only checked repository.full_name,
missing commits ingested by github_repo which store the repo name
in _repo instead.

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

crates/moments-core/src/presentation/github.rs

@@ -480,6 +480,7 @@ fn commit_reshape(event: &Event) -> TimelineItem {
         .get("repository")
         .and_then(|r| r.get("full_name"))
         .and_then(Value::as_str)
+        .or_else(|| p.get("_repo").and_then(Value::as_str))
         .unwrap_or("(unknown repo)");
     let author_login = p
         .get("author")