Enhance BatchRunner and AIAgent with new configuration options, default model now opus 4.6, default summarizer gemini flash 3

- Added `max_tokens`, `reasoning_config`, and `prefill_messages` parameters to `BatchRunner` and `AIAgent` for improved model response control.
- Updated CLI to support new options for reasoning effort and prefill messages from a JSON file.
- Modified example configuration files to reflect changes in default model and summary model.
- Improved error handling for loading prefill messages and reasoning configurations in the CLI.
- Updated documentation to include new parameters and usage examples.

cron/scheduler.py

@@ -40,7 +40,7 @@ def run_job(job: dict) -> tuple[bool, str, Optional[str]]:
         # Create agent with default settings
         # Jobs run in isolated sessions (no prior context)
         agent = AIAgent(
-            model=os.getenv("HERMES_MODEL", "anthropic/claude-sonnet-4"),
+            model=os.getenv("HERMES_MODEL", "anthropic/claude-opus-4.6"),
             quiet_mode=True,
             session_id=f"cron_{job_id}_{datetime.now().strftime('%Y%m%d_%H%M%S')}"
         )