Introduces a 'create_new_topic' tool to organize agent work into logical chapters in the UI.
Key changes:
- Added TopicManager singleton to track active session phase.
- Updated Scheduler to prioritize topic markers at the start of batches.
- Injected active topic context into prompt footers for model alignment.
- Removed 'Explain Before Acting' mandate in favor of semantic headers.
- Added behavioral eval to ensure model compliance with grouping.
