Remove user agent monkey-patching

Let truthbrush use its default configuration instead of overriding.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/poller.py

@@ -7,16 +7,8 @@ import tempfile
 import time
 from typing import Optional
 
-import truthbrush.api
 from truthbrush import Api
 
-# Override the default user agent to match the Chrome 136 TLS fingerprint
-# that curl_cffi uses (impersonate="chrome136")
-truthbrush.api.USER_AGENT = (
-    "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 "
-    "(KHTML, like Gecko) Chrome/136.0.0.0 Safari/537.36"
-)
-
 from .database import init_db, is_post_seen, mark_post_seen
 from .discord import send_post_to_discord
 from .media import process_media