[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/app-server/src/config_api.rs

@@ -130,7 +130,7 @@ impl ConfigApi {
             .unwrap_or_default()
     }
 
-    async fn load_latest_config(
+    pub(crate) async fn load_latest_config(
         &self,
         fallback_cwd: Option<PathBuf>,
     ) -> Result<Config, JSONRPCErrorError> {