skills/install.sh: also link trial set into the test-codex sandbox
Mirror the tc (~/.claude-test) wiring for tcx (CODEX_HOME=~/.codex-test): link experimental_skills/ into ~/.codex-test/skills on the all/codex targets, leaving the regular ~/.codex install untouched. Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>