Reduce the surface of collaboration modes (#20149)

Collaboration modes were slightly invasive both into ThreadManager
construction and ModelProvider

codex-rs/Cargo.lock

@@ -2977,9 +2977,7 @@ dependencies = [
  "codex-config",
  "codex-core",
  "codex-exec-server",
- "codex-features",
  "codex-login",
- "codex-models-manager",
  "codex-protocol",
  "codex-shell-command",
  "codex-utils-absolute-path",