Warn about ignored configuration settings (#44691)

## Why

Unrecognized settings can be silently ignored, leaving typos or deprecated configuration unnoticed.

## What changed

- Collect warnings for unrecognized fields in effective configuration and requirements layers, including unknown feature keys in configuration.
- Report sources and field names without configuration values, show up to three entries, and provide migration hints for `network_proxy`, `allowed_permissions`, and `include_view_image_tool`.
- Emit project-specific warnings when starting a thread and suppress repeated startup warnings in the app server and TUI.

## Testing

Add coverage for merged configuration, disabled layers, startup and project warning delivery, omission of configuration values, and warning deduplication.

GitOrigin-RevId: 464cef87882502b19865ae10b50b6f82defb7296

codex-rs/app-server/src/request_processors/thread_processor.rs

@@ -1424,10 +1424,23 @@ impl ThreadRequestProcessor {
                 .map_err(|err| config_load_error(&err))?;
         }
 
+        // Thread config can include project-local warnings absent at initialization.
+        let mut config_warnings = config
+            .startup_warnings
+            .iter()
+            .map(|summary| ConfigWarningNotification {
+                summary: summary.clone(),
+                details: None,
+                path: None,
+                range: None,
+            })
+            .collect::<Vec<_>>();
         if let Ok(Some(err)) =
             codex_core::check_execpolicy_for_warnings(&config.config_layer_stack).await
         {
-            let notification = crate::exec_policy_config_warning(&err);
+            config_warnings.push(crate::exec_policy_config_warning(&err));
+        }
+        for notification in config_warnings {
             if !initial_config_warnings.contains(&notification) {
                 listener_task_context
                     .outgoing