Use the API plugin marketplace for Amazon Bedrock (#34931)

## Why

Amazon Bedrock configurations can operate without Codex auth, so auth mode alone
cannot determine which curated plugin marketplace to expose.

## What changed

- Pass the resolved model provider into plugin configuration.
- Select `openai-api-curated` when the resolved provider is `amazon-bedrock`,
  while retaining API-key auth as a selection signal.
- Cover provider overrides and app-server plugin listing without an `auth.json`
  file.

GitOrigin-RevId: 972a22e19c41490d8b19d989da052302dc30e8f2

codex-rs/core-plugins/src/test_support.rs

@@ -213,8 +213,14 @@ pub(crate) async fn load_plugins_config(codex_home: &Path, cwd: &Path) -> Plugin
     .await
     .expect("config should load");
     let effective_config = config_layer_stack.effective_config();
+    let model_provider_id = effective_config
+        .get("model_provider")
+        .and_then(toml::Value::as_str)
+        .unwrap_or_default()
+        .to_string();
     PluginsConfigInput::new(
         config_layer_stack,
+        model_provider_id,
         feature_enabled(&effective_config, "plugins", /*default_enabled*/ true),
         feature_enabled(
             &effective_config,