fix(provider): honor NANOBOT_STREAM_IDLE_TIMEOUT_S in Codex provider

Every other streaming provider (anthropic, bedrock, openai_compat,
litellm) reads NANOBOT_STREAM_IDLE_TIMEOUT_S with a 90s default. The
Codex provider hardcoded 60s in _request_codex, so it could not be
tuned the same way and aborted streams sooner than its peers.

Read the same env var with the same default and pass it as the httpx
client timeout. The variable name and int parsing match anthropic /
openai_compat / bedrock verbatim.

#4009 normalized the error response when the timeout fires; this PR
fixes the timeout knob itself.

nanobot/providers/openai_codex_provider.py

@@ -5,6 +5,7 @@ from __future__ import annotations
 import asyncio
 import hashlib
 import json
+import os
 from collections.abc import Awaitable, Callable
 from typing import Any
 
@@ -177,7 +178,8 @@ async def _request_codex(
     on_content_delta: Callable[[str], Awaitable[None]] | None = None,
     on_tool_call_delta: Callable[[dict[str, Any]], Awaitable[None]] | None = None,
 ) -> tuple[str, list[ToolCallRequest], str]:
-    async with httpx.AsyncClient(timeout=60.0, verify=verify) as client:
+    idle_timeout_s = int(os.environ.get("NANOBOT_STREAM_IDLE_TIMEOUT_S", "90"))
+    async with httpx.AsyncClient(timeout=idle_timeout_s, verify=verify) as client:
         async with client.stream("POST", url, headers=headers, json=body) as response:
             if response.status_code != 200:
                 text = await response.aread()