Auto-saves every 3 seconds and on page unload. Restores the full
state (circuit, camera, custom components) on page load.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Add progressive puzzle mode alongside the existing sandbox:
- 8 levels from basic gates to 2-bit adder
- Truth table verification with pass/fail feedback
- Gate restrictions per level
- Custom components system (save circuits as reusable chips)
- Save/load circuits as JSON
- Level selection sidebar with difficulty ratings
- Mode toggle: Sandbox (free play) vs Puzzle (guided levels)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>