chore(makefile): decouple install-service from quality gates; drop agents-rename gate
install-service no longer invokes install-checks during the upgrade or
current install paths — it surprised users by running ruff/format/mypy/
layer-hygiene against the working tree at install time. install-checks
remains the canonical pre-merge gate via make ci / make verify.
The agents→talents rename has shipped, so the rename-guard gate is
permanent dead weight. Removes the Makefile target, the .PHONY entry,
the script, the install-checks invocation, and the doc references.
Co-Authored-By: Codex <codex@openai.com>