brainstorm

When this skill is invoked:

1. Parse the argument for an optional genre/theme hint (e.g., roguelike, space survival, cozy farming). If open or no argument, start from scratch.

2. Check for existing concept work:

   • Read design/gdd/game-concept.md if it exists (resume, don't restart)
   • Read design/gdd/game-pillars.md if it exists (build on established pillars)

3. Run through ideation phases interactively, asking the user questions at each phase. Do NOT generate everything silently — the goal is collaborative exploration where the AI acts as a creative facilitator, not a replacement for the human's vision.