docs: add comprehensive README with full project overview

Covers game modes, controls, gadget system, maps, level editor,
project structure, dev setup, API, and technical details.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

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+# ⚡ Logic Gates — Circuit Simulator RPG
+
+A logic gate circuit simulator combined with a Pokemon-style tile-based world. Players explore **Neon Town**, interact with NPCs, and craft logic circuits in a **Workshop** to solve puzzle doors and progress through the game.
+
+**Live:** [logic.montlab.dev](https://logic.montlab.dev)
+
+## 🎮 Game Modes
+
+### World Mode (exploration)
+- Walk around pixel-art maps rendered from PNG backgrounds
+- Talk to NPCs, read signs, enter buildings through doors
+- Find puzzle doors that require specific circuit outputs to unlock
+- Open your **backpack** to manage saved gadgets
+
+### Workshop Mode (circuit editor)
+- Full-featured logic gate simulator with drag-and-drop
+- Gates: AND, OR, NOT, NAND, NOR, XOR, INPUT, OUTPUT, CLOCK
+- Wire gates together by dragging between ports
+- Real-time simulation with GTKWave-style waveform viewer
+- Save circuits as **custom components** for reuse
+- Save circuits as **gadgets** to your backpack for use on puzzles
+
+## 🕹️ Controls
+
+### World
+| Key | Action |
+|-----|--------|
+| WASD / Arrows | Move |
+| E / Enter / Space | Interact with NPCs, signs, doors |
+| I | Open Backpack |
+| TAB | Open Workshop |
+| F3 | Toggle debug collision overlay |
+
+### Workshop
+| Key | Action |
+|-----|--------|
+| Click + Drag | Place and connect gates |
+| Shift + Drag | Cut wires / create bus connectors |
+| Mouse wheel | Zoom |
+| Arrows / +/- | Pan and zoom |
+| 0 | Reset camera |
+
+### Backpack
+| Key | Action |
+|-----|--------|
+| ↑↓ / WS | Navigate gadget list |
+| E / Enter | Select → Use / Toss |
+| I / ESC / B | Close |
+
+## 🎒 Gadget System
+
+Circuits become portable items:
+
+1. **Build** a circuit in the Workshop with INPUT and OUTPUT gates
+2. **Save as Gadget** (pink button, top-right) — names it and stores in your backpack
+3. **Use on puzzle doors** — the game runs your circuit's truth table against the puzzle's required outputs
+4. If outputs match → puzzle solved, door unlocks!
+
+## 🗺️ Maps
+
+| Map | Size | Description |
+|-----|------|-------------|
+| Neon Town | 20×18 | Hub town with buildings, NPCs, signs |
+| Circuit Lab | 10×12 | Professor's lab with workshop tables |
+| House Interior | 8×8 | Generic house (WIP) |
+| Route 1 | 20×36 | Path to next area (WIP) |
+
+### Bidirectional Door System
+Every door is a two-way link with explicit coordinates — entering a building through a specific door returns you to that exact door when you exit. `spawn` only exists on the starting map (Neon Town).
+
+## 🛠️ Level Editor
+
+Standalone editor at `/editor.html` for visually editing maps:
+
+- **Wall painting** — click/drag to paint collision masks
+- **Entity placement** — NPCs, exits, interactions, spawn points
+- **🔗 Bi-Link tool** — create bidirectional door links between maps in one click
+- **Properties panel** — edit entity properties (dialog, facing, target map/coords)
+- **Zoom/pan** — mouse wheel, +/-, arrows, right-click drag
+- **Server save/load** — saves directly to `maps.js` via API
+- **Keyboard shortcuts** — 1-7 for tools, Ctrl+S to save, Delete to remove
+
+## 📁 Project Structure
+
+```
+├── index.html              # Main game page
+├── editor.html             # Standalone level editor
+├── server.js               # Node.js server (static + API)
+├── Dockerfile              # Docker build (node:20-alpine)
+├── assets/
+│   ├── map/                # PNG map backgrounds (lab, pallet-town, house, route-1)
+│   └── character/          # Player sprites (32×32, 4 directions × 3 frames)
+│       └── npcs/           # NPC sprites (16×16)
+├── css/
+│   └── style.css           # Workshop UI styles
+├── js/
+│   ├── app.js              # Entry point, wires everything together
+│   ├── state.js            # Circuit editor state
+│   ├── gates.js            # Gate creation and evaluation
+│   ├── connections.js      # Wire/connection logic
+│   ├── renderer.js         # Circuit editor canvas rendering
+│   ├── events.js           # Circuit editor mouse/keyboard events
+│   ├── components.js       # Custom component system (save/eval/edit)
+│   ├── saveLoad.js         # Circuit serialization
+│   ├── levels.js           # Puzzle level definitions
+│   ├── constants.js        # Shared constants
+│   └── world/
+│       ├── gameMode.js     # Mode coordinator (world ↔ workshop)
+│       ├── maps.js         # Map definitions (walls, exits, NPCs, interactions)
+│       ├── sprites.js      # PNG asset loading and drawing
+│       ├── worldRenderer.js# World canvas rendering (map, NPCs, player, HUD, debug)
+│       ├── worldInput.js   # World keyboard input (movement, interaction)
+│       ├── worldState.js   # World game state (player, dialog, puzzles, gadgets)
+│       └── inventory.js    # Gadget backpack (data model + full-screen UI)
+```
+
+## 🚀 Development
+
+### Run locally
+```bash
+npm start          # or: node server.js
+# Open http://localhost:3000
+```
+
+### Deploy (Docker via Coolify)
+```bash
+docker build -t logic-gates .
+docker run -p 3000:3000 logic-gates
+```
+
+Deployed automatically via Coolify on Hetzner at `logic.montlab.dev`.
+
+### API Endpoints
+| Method | Endpoint | Description |
+|--------|----------|-------------|
+| GET | `/api/maps` | Get current maps.js content |
+| PUT | `/api/maps` | Update maps.js (creates .bak backup) |
+
+## 🔧 Technical Details
+
+- **Rendering**: Vanilla Canvas 2D, no frameworks
+- **Modules**: ES6 modules (`type="module"`)
+- **Tile system**: 16px native tiles, 3× scale = 48px on screen
+- **Collision**: `Set<"x,y">` for O(1) wall lookups
+- **Player sprite**: 32×32 native, drawn at 48×48 (same visual size as 16×16 NPC sprites at 48×48)
+- **Camera**: Follows player, centered on screen
+- **Movement**: Interpolated tile-based (0.15s per tile)
+- **Circuit evaluation**: Fixed-point iteration (max 20 passes) — supports latches/flip-flops