## Why
Symlinked skills have a canonical `SKILL.md` path that can differ from the path
under the configured skill root. A catalog entry that advertises the discovery
path must still select the canonical skill.
## What changed
- Track each loaded skill's discovery path alongside its canonical identity.
- Render discovery paths in the skill catalog and accept either form for
structured selections and linked skill mentions.
- Preserve enabled-state checks, deduplication, and product filtering when
resolving discovery paths.
## Testing
Added loader, catalog, mention-resolution, and end-to-end turn coverage for
skills discovered through directory symlinks.
GitOrigin-RevId: bae539b766cc3782c7c121a4276c337699cbb509