Pin Codex development tool paths

Pinning prevents trusted rules from matching an unexpected executable with the same name.

From the development shell's repository root:

mkdir -p ~/.codex/rules
python3 scripts/setup_dev_execpolicy.py \
  > ~/.codex/rules/codex_dev_tool_paths.rules

This pins binaries for the repository's development rules. Rules load when a Codex session starts.