Remove redundant Codex Apps manager flag (#29518)

## Why

Codex Apps server admission is already decided before
`McpConnectionManager` is constructed. `effective_mcp_servers` and
`effective_mcp_servers_from_configured` remove the server when the apps
feature or required authentication is unavailable, so storing the same
decision on the manager duplicates state that can drift from the
effective server map.

## What changed

- Remove `host_owned_codex_apps_enabled` from `McpConnectionManager` and
its constructor.
- Identify the host-owned Codex Apps server by its reserved server name
once it is present in the effective server map.
- Remove the now-unused flag calculations and constructor arguments from
production and test callsites.

codex-rs/codex-mcp/src/mcp/mod.rs

@@ -277,7 +277,6 @@ pub async fn read_mcp_resource(
     uri: &str,
 ) -> anyhow::Result<ReadResourceResult> {
     let mut mcp_servers = effective_mcp_servers(config, auth);
-    let host_owned_codex_apps_enabled = host_owned_codex_apps_enabled(config, auth);
     mcp_servers.retain(|name, _| name == server);
     let auth_statuses = compute_auth_statuses(
         mcp_servers.iter(),
@@ -302,7 +301,6 @@ pub async fn read_mcp_resource(
         runtime_context,
         config.codex_home.clone(),
         codex_apps_tools_cache_key(auth),
-        host_owned_codex_apps_enabled,
         config.prefix_mcp_tool_names,
         config.client_elicitation_capability.clone(),
         /*supports_openai_form_elicitation*/ false,
@@ -337,7 +335,6 @@ pub async fn collect_mcp_server_status_snapshot_with_detail(
     detail: McpSnapshotDetail,
 ) -> McpServerStatusSnapshot {
     let mcp_servers = effective_mcp_servers(config, auth);
-    let host_owned_codex_apps_enabled = host_owned_codex_apps_enabled(config, auth);
     let tool_plugin_provenance = tool_plugin_provenance(config);
     if mcp_servers.is_empty() {
         return McpServerStatusSnapshot {
@@ -377,7 +374,6 @@ pub async fn collect_mcp_server_status_snapshot_with_detail(
         runtime_context,
         config.codex_home.clone(),
         codex_apps_tools_cache_key(auth),
-        host_owned_codex_apps_enabled,
         config.prefix_mcp_tool_names,
         config.client_elicitation_capability.clone(),
         /*supports_openai_form_elicitation*/ false,