feat: persist circuit and components to localStorage

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>

js/app.js

@@ -2,9 +2,21 @@
 import { initRenderer } from './renderer.js';
 import { initEvents } from './events.js';
 import { initPuzzleUI } from './puzzleUI.js';
+import { loadFromStorage, startAutoSave } from './saveLoad.js';
+import { updateComponentButtons } from './components.js';
+import { evaluateAll } from './gates.js';
 
 document.addEventListener('DOMContentLoaded', () => {
     initRenderer();
     initEvents();
     initPuzzleUI();
+
+    // Restore previous session from localStorage
+    if (loadFromStorage()) {
+        updateComponentButtons();
+        evaluateAll();
+    }
+
+    // Auto-save every 3 seconds + on page unload
+    startAutoSave(3000);
 });