Fix Codex Apps auth elicitation hang (#29615)

## Summary
- Require the reserved Codex Apps MCP server name to be present in the
connection manager before treating it as host-owned.
- Update auth elicitation tests to model an installed host-owned Codex
Apps server without sending startup events to the test session.

## Why
PR #29518 replaced the old host-owned flag with a name-only check. That
made non-host-owned tests with the reserved codex_apps name enter auth
elicitation and wait forever for a response.

codex-rs/codex-mcp/src/connection_manager.rs

@@ -391,7 +391,7 @@ impl McpConnectionManager {
     }
 
     pub fn is_host_owned_codex_apps_server(&self, server_name: &str) -> bool {
-        server_name == CODEX_APPS_MCP_SERVER_NAME
+        server_name == CODEX_APPS_MCP_SERVER_NAME && self.server_metadata.contains_key(server_name)
     }
 
     pub fn set_approval_policy(&self, approval_policy: &Constrained<AskForApproval>) {