fix: clarify the value of SkillMetadata.path (#12729)

Rename `SkillMetadata.path` to `SkillMetadata.path_to_skills_md` for
clarity.

Would ideally change the type to `AbsolutePathBuf`, but that can be done
later.

codex-rs/tui/src/bottom_pane/mod.rs

@@ -1495,7 +1495,7 @@ mod tests {
                 dependencies: None,
                 policy: None,
                 permissions: None,
-                path: PathBuf::from("test-skill"),
+                path_to_skills_md: PathBuf::from("test-skill"),
                 scope: SkillScope::User,
             }]),
         });