Add safety check notification and error handling (#19055)

Adds a new app-server notification that fires when a user account has
been flagged for potential safety reasons.

codex-rs/codex-api/src/error.rs

@@ -27,6 +27,8 @@ pub enum ApiError {
     RateLimit(String),
     #[error("invalid request: {message}")]
     InvalidRequest { message: String },
+    #[error("cyber policy: {message}")]
+    CyberPolicy { message: String },
     #[error("server overloaded")]
     ServerOverloaded,
 }