core/tui: non-blocking MCP startup (#6334)

This makes MCP startup not block TUI startup. Messages sent while MCPs
are booting will be queued.


https://github.com/user-attachments/assets/96e1d234-5d8f-4932-a935-a675d35c05e0


Fixes #6317

---------

Co-authored-by: pakrym-oai <pakrym@openai.com>

codex-rs/mcp-server/src/codex_tool_runner.rs

@@ -258,6 +258,9 @@ async fn run_codex_tool_session_inner(
                     EventMsg::AgentReasoningDelta(_) => {
                         // TODO: think how we want to support this in the MCP
                     }
+                    EventMsg::McpStartupUpdate(_) | EventMsg::McpStartupComplete(_) => {
+                        // Ignored in MCP tool runner.
+                    }
                     EventMsg::AgentMessage(AgentMessageEvent { .. }) => {
                         // TODO: think how we want to support this in the MCP
                     }