Drop skill descriptions before omitting catalog entries (#34738)

## What changed

When even the minimum skill catalog exceeds its metadata budget, render each
included entry without its description. This allows more skill names and
locators to fit before the remaining entries are omitted.

## Testing

Add coverage for extreme budget pressure and verify both the extension and
production-turn catalogs omit descriptions while staying within budget.

GitOrigin-RevId: 72cec10e9587beabbd3d8c6d53b931deb76824e6

codex-rs/core/tests/suite/skills_extension.rs

@@ -141,6 +141,9 @@ async fn production_turn_scales_extension_catalog_from_resolved_model_window() -
             .count();
 
         assert!(catalog_text.contains("additional skills omitted"));
+        assert!(!catalog_text.contains(
+            "A description long enough to keep the catalog under sustained budget pressure."
+        ));
         assert!(metadata_cost <= expected_budget);
         included_counts.push(included_count);
     }