Adds the spike's layout, flow, hardcoded values, and done criteria so
implementation has a clear target. No code yet.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Architectural design (PLAN.md) and project intro committed before any
implementation begins.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>