Deprecation warning links to removed docs anchor docs/config.md#feature-flags

What version of Codex is running?

codex-cli 0.104.0

What issue are you seeing?

Deprecation notices still point users to:

https://github.com/openai/codex/blob/main/docs/config.md#feature-flags

But docs/config.md no longer has a #feature-flags section (it is now a short pointer page to developers.openai.com docs), so the warning sends users to a stale anchor.

Example warning text:

collab is deprecated. Use [features].multi_agent instead.
Enable it with --enable multi_agent or [features].multi_agent in config.toml. See https://github.com/openai/codex/blob/main/docs/config.md#feature-flags for details.

Steps to reproduce

1. Use a legacy feature key (example: [features] collab = true).
2. Start Codex.
3. Observe the deprecation warning details link.
4. Open the linked URL.

Expected behavior

Deprecation warnings should link to a current docs location that actually contains feature-flag guidance (for example the developers docs config reference), not a removed GitHub anchor.

Additional context

The stale link string appears to be constructed in codex-rs/core/src/features.rs deprecation notice details.