[mcp] Support MCP Apps part 2 - Add meta to mcp tool call result. (#16465)

- [x] Add meta to mcp tool call result.

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

@@ -5048,6 +5048,9 @@ pub struct McpToolCallResult {
     // representations). Using `JsonValue` keeps the payload wire-shaped and easy to export.
     pub content: Vec<JsonValue>,
     pub structured_content: Option<JsonValue>,
+    #[serde(rename = "_meta")]
+    #[ts(rename = "_meta")]
+    pub meta: Option<JsonValue>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]