fix: add runAs: subagent to SKILL.md frontmatter

When installed via the bundled shell scripts, Reasonix reads SKILL.md
directly from ~/.reasonix/skills/cli-anything/SKILL.md. Without runAs:
subagent in the frontmatter, the skill defaults to inline mode, which
runs the entire CLI-Anything workflow in the parent session instead of
in an isolated sub-agent as documented in README.md.

The install_skill API path already included this field (passed as a
parameter), but the source SKILL.md file was missing it, causing
inconsistent behavior between the two installation methods.