fix: use absolute skill_dir for external skills (#10313) (#10587)

_load_skill_payload() reconstructed skill_dir as SKILLS_DIR / relative_path,
which is wrong for external skills from skills.external_dirs — they live
outside SKILLS_DIR entirely. Scripts and linked files failed to load.

Fix: skill_view() now includes the absolute skill_dir in its result dict.
_load_skill_payload() uses that directly when available, falling back to
the SKILLS_DIR-relative reconstruction only for legacy responses.

Closes #10313

tools/skills_tool.py

@@ -1263,6 +1263,7 @@ def skill_view(name: str, file_path: str = None, task_id: str = None) -> str:
             "related_skills": related_skills,
             "content": content,
             "path": rel_path,
+            "skill_dir": str(skill_dir) if skill_dir else None,
             "linked_files": linked_files if linked_files else None,
             "usage_hint": "To view linked files, call skill_view(name, file_path) where file_path is e.g. 'references/api.md' or 'assets/config.yaml'"
             if linked_files