Add optional tool context to request_user_input

Add optional tool/arguments fields to request_user_input events and app-server tool/requestUserInput params, then wire MCP approval flows to populate and forward them.

codex-rs/app-server-protocol/schema/json/v1/ResumeConversationResponse.json

@@ -1486,6 +1486,7 @@
         },
         {
           "properties": {
+            "arguments": true,
             "call_id": {
               "description": "Responses API call id for the associated tool call, if available.",
               "type": "string"
@@ -1496,6 +1497,12 @@
               },
               "type": "array"
             },
+            "tool": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "turn_id": {
               "default": "",
               "description": "Turn ID that this request belongs to. Uses `#[serde(default)]` for backwards compatibility.",