fix(setup): align braintrust skill name with install path

Rename the generated skill frontmatter from braintrust-cli to braintrust so installed skills match the parent directory name used by agent integrations.

Add a setup regression test to ensure future skill renders keep the expected frontmatter name and avoid skill conflict warnings.

Author: AbhiPrasad

skills/shared/skill_frontmatter.md

@@ -1,5 +1,5 @@
 ---
-name: braintrust-cli
+name: braintrust
 version: 1.0.0
 description: Use the Braintrust `bt` CLI for projects, traces, prompts, and key Braintrust workflows.
 ---

src/setup/mod.rs

@@ -3709,6 +3709,12 @@ mod tests {
         assert!(root.join(".cursor/skills").exists());
     }
 
+    #[test]
+    fn rendered_skill_frontmatter_name_matches_braintrust_directory() {
+        let content = render_braintrust_skill();
+        assert!(content.starts_with("---\nname: braintrust\n"));
+    }
+
     #[test]
     fn docs_cache_has_required_files_checks_workflows_and_sql_reference() {
         let unique = SystemTime::now()