[mcp] Improve custom MCP elicitation (#15800)

- [x] Support don't ask again for custom MCP tool calls.
- [x] Don't run arc in yolo mode.
- [x] Run arc for custom MCP tools in always allow mode.

codex-rs/core/tests/suite/sqlite_state.rs

@@ -375,6 +375,7 @@ async fn mcp_call_marks_thread_memory_mode_polluted_when_configured() -> Result<
                 disabled_tools: None,
                 scopes: None,
                 oauth_resource: None,
+                tools: HashMap::new(),
             },
         );
         config