Show spawned agent model and effort in TUI (#14273)

- include the requested sub-agent model and reasoning effort in the
spawn begin event\n- render that metadata next to the spawned agent name
and role in the TUI transcript

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -6180,10 +6180,16 @@
               "description": "Identifier for the collab tool call.",
               "type": "string"
             },
+            "model": {
+              "type": "string"
+            },
             "prompt": {
               "description": "Initial prompt sent to the agent. Can be empty to prevent CoT leaking at the beginning.",
               "type": "string"
             },
+            "reasoning_effort": {
+              "$ref": "#/definitions/ReasoningEffort"
+            },
             "sender_thread_id": {
               "allOf": [
                 {
@@ -6202,7 +6208,9 @@
           },
           "required": [
             "call_id",
+            "model",
             "prompt",
+            "reasoning_effort",
             "sender_thread_id",
             "type"
           ],