fix: Remove hard-coded token limits on LLM responses

- Add max_response_tokens config (8192) to LLMConfig
- Use config value in router.py instead of hardcoded 500
- Update base.py default from 300 to 8192
- Lets LLM generate full responses; chunker handles size limits

Fixes truncated responses like Here are three nodes in the freq

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

meshai/config.py

@@ -94,6 +94,7 @@ class LLMConfig:
     base_url: str = "https://api.openai.com/v1"
     model: str = "gpt-4o-mini"
     timeout: int = 30
+    max_response_tokens: int = 8192  # Let LLM generate full responses; chunker handles size
 
     system_prompt: str = (
         "RESPONSE RULES:\n"