docs: link companion datasets in README front-matter

datasets: lists the two companion dataset repos so the Hub renders
them as cards on the Space page (and so the link is explicit rather
than relying on auto-parse from hardcoded repo IDs in app.py /
leaderboard.py).

- HuggingAI4Engineering/cadgenbench-submissions: the results +
per-submission report dataset the leaderboard reads from.
- HuggingAI4Engineering/cadgenbench-data: the public fixture inputs.

cadgenbench-data-gt is omitted on purpose (permanently private).

README.md

@@ -9,6 +9,9 @@ pinned: true
 license: apache-2.0
 hf_oauth: true
 short_description: Leaderboard for AI-driven CAD generation
+datasets:
+  - HuggingAI4Engineering/cadgenbench-submissions
+  - HuggingAI4Engineering/cadgenbench-data
 ---
 
 # CADGenBench Leaderboard