feat(cli): graph-report titles + JSON warning; wire recommend/cocited (U-1,U-3,U-4,C-9)

- U-1: 'graph report' shows the paper title next to each in-KB hub (dangling
  OpenAlex-id hubs are flagged), instead of bare ids.
- U-3: '--json' now includes a 'small_corpus_warning' field (null unless below
  graph_min_corpus_size) instead of silently dropping the warning.
- C-9: new 'codex discover recommend <id>' wires semanticscholar.fetch_recommendations
  (was implemented + tested but unreachable).
- U-4: new 'codex graph cocited <id>' wires graph.find_co_cited (likewise).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/graph/test_cli.py

@@ -28,9 +28,11 @@ def _make_conn_cm(conn: MagicMock):
 
 
 def _make_conn_with_paper_ids(*paper_ids: str) -> MagicMock:
-    """Mock conn that returns paper rows for SELECT id FROM papers."""
+    """Mock conn that returns paper rows for SELECT id, title FROM papers."""
     conn = MagicMock()
-    conn.execute.return_value.fetchall.return_value = [{"id": pid} for pid in paper_ids]
+    conn.execute.return_value.fetchall.return_value = [
+        {"id": pid, "title": f"Title of {pid}"} for pid in paper_ids
+    ]
     return conn