chore: debug log for untrusted absolute skill paths; drop misleading test patch

Review findings: (a) an absolute path outside trusted roots passes
through unchanged and gets rejected downstream by skill_view — add a
debug log at the pass-through so the cron 'skill not found' symptom is
diagnosable next time; (b) test_relative_path_unchanged patched
get_skills_dir although the relative branch early-returns before any
root lookup — drop the misleading patch.

agent/skill_utils.py

@@ -556,6 +556,11 @@ def normalize_skill_lookup_name(identifier: str) -> str:
     try:
         return str(identifier_path.resolve().relative_to(primary_root.resolve()))
     except Exception:
+        logger.debug(
+            "Skill identifier %r is an absolute path outside trusted skills "
+            "roots — passing through unchanged (skill_view will reject it)",
+            raw_identifier,
+        )
         return raw_identifier