fix(minimax): add TTS options docs to canonical SKILL.md source

#360 added the "TTS options" section to skills/cli-anything-minimax/SKILL.md,
which is a generated mirror produced by .github/scripts/sync_root_skills.py
from minimax/agent-harness/cli_anything/minimax/skills/SKILL.md. The source
was never updated, so validate_root_skills.py failed on main.

Add the section to the canonical source. The mirror is unchanged, so the
documentation added in #360 is preserved verbatim. Note that running
sync_root_skills.py alone -- as the validator's error message suggests --
would have deleted those lines instead.