feat: add Pokemon-style world mode with workshop integration

Two-mode game: explore a tile-based cyberpunk world, then enter
Workshop mode (the existing circuit editor) to craft components.

New modules (js/world/):
- sprites.js: programmatic pixel-art renderer (16x16 tiles, 3x scale)
- maps.js: tile-based map definitions (lab + town)
- worldState.js: player position, inventory, dialog, puzzle state
- worldRenderer.js: camera-following world renderer on shared canvas
- worldInput.js: WASD movement, E interaction, dialog system
- gameMode.js: central mode switcher (world ↔ workshop)

Changes to existing code:
- app.js: boots into world mode, registers circuit editor for workshop
- renderer.js: circuit draw loop now stoppable (start/stopCircuitLoop)
- index.html: added "Back to World" button for workshop mode

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

js/renderer.js

@@ -6,6 +6,8 @@ import { getGateLabel, drawWaveLabels, drawWaveforms } from './waveform.js';
 import { getBusPairs } from './bus.js';
 
 let canvas, ctx;
+let circuitAnimFrameId = null;
+let rendererInitialized = false;
 
 /**
  * Read the value arriving at an input port by looking up the source gate/port.
@@ -25,8 +27,23 @@ export function initRenderer() {
     canvas = document.getElementById('canvas');
     ctx = canvas.getContext('2d');
     resize();
-    window.addEventListener('resize', resize);
-    requestAnimationFrame(draw);
+    if (!rendererInitialized) {
+        window.addEventListener('resize', resize);
+        rendererInitialized = true;
+    }
+    startCircuitLoop();
+}
+
+export function startCircuitLoop() {
+    if (circuitAnimFrameId) return; // already running
+    circuitAnimFrameId = requestAnimationFrame(draw);
+}
+
+export function stopCircuitLoop() {
+    if (circuitAnimFrameId) {
+        cancelAnimationFrame(circuitAnimFrameId);
+        circuitAnimFrameId = null;
+    }
 }
 
 export function resize() {
@@ -646,5 +663,5 @@ function draw() {
         drawWaveforms();
     }
 
-    requestAnimationFrame(draw);
+    circuitAnimFrameId = requestAnimationFrame(draw);
 }