Add Pokemon-style inventory where players save crafted circuits as
"gadgets" in a backpack. Gadgets can be used on puzzle doors to solve
them by testing their truth table against required outputs.
New files:
- js/world/inventory.js: gadget data model, backpack UI (list with
scroll, action menu, detail panel), keyboard navigation
Changes:
- Workshop gets "Save as Gadget" button (pink, top-right)
- I key opens backpack overlay in world mode
- Puzzle doors open backpack to select a gadget to try
- HUD shows gadget count instead of old component count
- worldState gains gadgets[] array
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
