- Add generateSubtasksFromPlanning function to generate subtasks from planning session key deliverables
- Add POST /planning/start-breakdown and POST /planning/create-tasks API routes
- Add startPlanningBreakdown and createTasksFromPlanning frontend API functions
- Extend PlanningModeModal with Break into Tasks UI and subtask editing (drag-and-drop, dependency validation)
- Add comprehensive tests for generateSubtasksFromPlanning with edge cases
- Document planning mode multi-task creation feature in AGENTS.md