Honor managed permission profiles in network proxy resolution (#34436)

## Why

Permission profiles defined by `requirements.toml` can be selected as active,
but their network configuration was not included when resolving the network
proxy specification for that selection.

## What changed

Merge managed permission profiles from `requirements.toml` with configured
profiles before looking up the active profile's network proxy settings.

## Testing

- Verify config loading retains the proxy settings of an active managed
  profile.
- Verify `turn/start` accepts a managed profile with network settings.

GitOrigin-RevId: 3374f82a8fb0ce8f338fa2cea77c28ea2eb89636

codex-rs/core/src/config/mod.rs

@@ -4204,8 +4204,12 @@ impl Config {
                         ),
                     )
                 })?;
-            let mut configured_network_proxy_config = network_proxy_config_for_profile_selection(
+            let permissions = merge_managed_permission_profiles(
                 cfg.permissions.as_ref(),
+                self.config_layer_stack.requirements_toml(),
+            )?;
+            let mut configured_network_proxy_config = network_proxy_config_for_profile_selection(
+                permissions.as_ref(),
                 active_permission_profile.id.as_str(),
             )?;
             if self.features.enabled(Feature::NetworkProxy)