## Why
Enterprise-managed hook policy needs a narrow way to require Codex to
ignore user-controlled lifecycle hooks without adopting the broader
trust-precedence model from earlier hook work. This keeps the policy
anchored in `requirements.toml`, so admins can opt into managed hooks
only while normal `config.toml` files cannot enable the restriction
themselves.
## What changed
- Added `allow_managed_hooks_only` to the requirements data flow and
preserved explicit `false` values.
- Also adds it to /debug-config
- Marked MDM, system, and legacy managed config layers as managed for
hook discovery.
- Updated hook discovery so `allow_managed_hooks_only = true`:
- keeps managed requirements hooks and managed config-layer hooks,
- skips user/project/session `hooks.json` and `[hooks]` entries with
concise startup warnings,
- skips current unmanaged plugin hooks,
- ignores any `allow_managed_hooks_only` key placed in ordinary
`config.toml` layers.