docs: add leaderboard discovery tags to README front-matter

tags: surfaces this Space in the Hub's leaderboard discovery filter
(huggingface.co/spaces?other=leaderboard) and faceted searches by
modality, submission type, and eval type.

The set blends the empirical vocabulary across the top 50
leaderboard-tagged Spaces with three truthful novel descriptors:
modality:3d (closest existing values are modality:text / tools,
neither accurate for STEP geometry), eval:cad (paired with
eval:generation so the standard "generation" chip also surfaces
us), and judge:auto (eval is metric-based, no LLM/human judge).

README.md

@@ -12,6 +12,15 @@ short_description: Leaderboard for AI-driven CAD generation
 datasets:
   - HuggingAI4Engineering/cadgenbench-submissions
   - HuggingAI4Engineering/cadgenbench-data
+tags:
+  - leaderboard
+  - modality:3d
+  - submission:automatic
+  - test:private
+  - language:english
+  - eval:generation
+  - eval:cad
+  - judge:auto
 ---
 
 # CADGenBench Leaderboard