Feat: add isOther to question returned by request user input tool (#9890)

### Summary
Add `isOther` to question object from request_user_input tool input and
remove `other` option from the tool prompt to better handle tool input.

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -2420,6 +2420,8 @@ pub struct ToolRequestUserInputQuestion {
     pub id: String,
     pub header: String,
     pub question: String,
+    #[serde(default)]
+    pub is_other: bool,
     pub options: Option<Vec<ToolRequestUserInputOption>>,
 }