/sprint

[Agent] Organise user stories into balanced sprints

Spawn the `dev-team:sprint` agent (model: sonnet) to plan sprints.

The agent is a Sprint Planning Specialist who:
- Uses maximum 11 points per sprint
- Balances MoSCoW priorities (60% Must, 25% Should, 15% Could)
- Reads stories from `docs/STORIES/`
- Creates sprint files in `docs/SPRINTS/`

**User's Request:**
$ARGUMENTS