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/router.py

@@ -643,7 +643,7 @@ class MessageRouter:
             response = await self.llm.generate(
                 messages=history,
                 system_prompt=system_prompt,
-                max_tokens=500,
+                max_tokens=self.config.llm.max_response_tokens,
             )
         except asyncio.TimeoutError:
             logger.error("LLM request timed out")