## Why
Executor-backed skills can include bundled scripts, so skill readers need the
skill directory in the executor filesystem to locate them.
## What changed
- Add `skill_root` to `skills.read` responses for executor-backed skills.
- Derive the root from the parent directory of the skill's main resource and
omit the field for other skill authorities.
## Testing
- Verify executor skill reads return the expected root for both `SKILL.md` and
a referenced resource.
GitOrigin-RevId: b7035c7e2e62155890795fb508fefe3a1c17805b