Trust prompt for skills that resolve outside trusted skill directories.
When a /skill:<name> invocation reads a SKILL.md whose resolved path (via
symlink) falls outside every trusted skill root, load_skill_content refuses
the read. Rather than forcing the user to quit, edit env/config, and relaunch,
this non-blocking modal asks for an in-the-moment decision. Allowing persists
the resolved target directory to the skill trust store.