Expose configured permission profiles as ACP modes #519

Codex supports user-defined permission profiles, but codex-acp does not expose them in the ACP mode selector. Users should be able to select their configured profiles directly from clients such as Zed.

Please discover allowed, user-defined permission profiles and expose them as additional ACP modes, including their configured descriptions.

Expected behavior:

• Show allowed custom profiles alongside the existing modes.
• Reflect the active profile when starting or resuming a session.
• Apply the selected profile to subsequent turns, preserving its effective approval policy and supporting additional workspace roots.
• Exclude disallowed profiles and avoid duplicating built-in profiles.
• Preserve the behavior of the existing modes.

Related to #310.