- Directly set chat_template to known template names (qwen3, qwen, llama3, etc.)
  instead of trying to load non-existent HuggingFace tokenizers
- Add use_manual condition to use manual formatting when chat_template is set
  but hf_tokenizer is None (applies to both generate_chat and generate_chat_stream)
- This ensures GGUF models loaded from URLs with known templates use proper
  <|im_start|> formatting instead of failing on create_chat_completion