feat(app-server): add v2 deprecation notice (#8285)

Add a v2 event for deprecation notices so we can get rid of
`codex/event/deprecation_notice`.

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

@@ -1893,6 +1893,16 @@ pub struct AccountLoginCompletedNotification {
     pub error: Option<String>,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct DeprecationNoticeNotification {
+    /// Concise summary of what is deprecated.
+    pub summary: String,
+    /// Optional extra guidance, such as migration steps or rationale.
+    pub details: Option<String>,
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;