Stop Claude Preambles With Positive Instructions

Because Claude tends to be chatty at the beginning of responses, and assistant prefills like "Here is the requested summary:\n" are deprecated in newer models, use direct system prompt instructions paired with XML output tags to eliminate preambles.

System: Respond directly without preamble. Do not start with phrases like "Here is...", "Based on...", etc. Place the raw output strictly inside <output_config> tags. User: Generate an nginx reverse-proxy block for port 8080.