chore(app-server) world-writable windows notification (#6880)

## Summary
On app-server startup, detect whether the experimental sandbox is
enabled, and send a notification .

**Note**
New conversations will not respect the feature because we [ignore cli
overrides in
NewConversation](a75321a64c/codex-rs/app-server/src/codex_message_processor.rs (L1237-L1252)).
However, this should be okay, since we don't actually use config for
this, we use a [global
variable](87cce88f48/codex-rs/core/src/safety.rs (L105-L110)).
We should carefully unwind this setup at some point.


## Testing
- [ ] In progress: testing locally

---------

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

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -494,6 +494,9 @@ server_notification_definitions! {
     ReasoningSummaryPartAdded => "item/reasoning/summaryPartAdded" (v2::ReasoningSummaryPartAddedNotification),
     ReasoningTextDelta => "item/reasoning/textDelta" (v2::ReasoningTextDeltaNotification),
 
+    /// Notifies the user of world-writable directories on Windows, which cannot be protected by the sandbox.
+    WindowsWorldWritableWarning => "windows/worldWritableWarning" (v2::WindowsWorldWritableWarningNotification),
+
     #[serde(rename = "account/login/completed")]
     #[ts(rename = "account/login/completed")]
     #[strum(serialize = "account/login/completed")]