Fix Codex hooks config schema

[CryptoJones]

Summary

• write Codex hook installs under the current root hooks object
• migrate legacy root-level hook events into hooks while preserving user hook groups
• bump patch version to 3.7.1 and document the fix

Tests

• uv run python -m pytest tests/test_agents.py -k codex
• uv run python -m pytest tests/test_cli.py::test_version_is_set
• uv run python -m ruff check src/omind/agents.py tests/test_agents.py
• git diff --check