Plot: Create Idea

Create a plan for review: idea branch, plan file, and draft PR.

Input: $ARGUMENTS in the format <slug>: <title description>

Example: /plot-idea sse-backpressure: Handle SSE client disconnects gracefully

Setup

Add a ## Plot Config section to the adopting project's CLAUDE.md:

## Plot Config
- **Project board:** <your-project-name> (#<number>)  <!-- optional, for `gh pr edit --add-project` -->
- **Branch prefixes:** idea/, feature/, bug/, docs/, infra/
- **Plan directory:** docs/plans/
- **Active index:** docs/plans/active/
- **Delivered index:** docs/plans/delivered/