_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