Remove unused LLMConfig from BotConfig

LLMConfig was stored in BotConfig but never accessed after
construction — LLMClient receives it directly.

https://claude.ai/code/session_01AKXQBuVBsW7J1YbukDiQ7A

python/signal_bot/main.py

@@ -118,7 +118,6 @@ def main(
     config = BotConfig(
         signal_api_url=signal_api_url,
         phone_number=phone_number,
-        llm=llm_config,
         inventory_file=inventory_file,
     )
 

python/signal_bot/models.py

@@ -81,5 +81,4 @@ class BotConfig(BaseModel):
 
     signal_api_url: str
     phone_number: str
-    llm: LLMConfig
     inventory_file: str = "van_inventory.json"