## Implementation
- [x] Update `write_summary` title handling to rename the current meeting note for non-empty title values.
- [x] Keep existing title behavior when the title parameter is omitted or blank.
- [x] Update summary-agent instructions and tool description for generated default titles.
- [x] Add focused tests for rename, omitted title, blank title, and instructions.
- [x] Validate with focused tests, `dotnet test MeetingAssistant.slnx`, and `openspec validate allow-summary-title-rename --strict`.