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/codex_app_server_protocol.schemas.json

@@ -3445,6 +3445,7 @@
         },
         {
           "properties": {
+            "arguments": true,
             "call_id": {
               "description": "Responses API call id for the associated tool call, if available.",
               "type": "string"
@@ -3455,6 +3456,12 @@
               },
               "type": "array"
             },
+            "tool": {
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "turn_id": {
               "default": "",
               "description": "Turn ID that this request belongs to. Uses `#[serde(default)]` for backwards compatibility.",
@@ -8964,6 +8971,7 @@
       "$schema": "http://json-schema.org/draft-07/schema#",
       "description": "EXPERIMENTAL. Params sent with a request_user_input event.",
       "properties": {
+        "arguments": true,
         "itemId": {
           "type": "string"
         },
@@ -8976,6 +8984,12 @@
         "threadId": {
           "type": "string"
         },
+        "tool": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "turnId": {
           "type": "string"
         }