Overdrive laser demo, deep link support, and split-compare fix

Demo:
- Laser-etched "Paul Bakaus" signature drawn in real-time on dark
  surface, adapted from pbakaus/shaders laser-precision
- Two-canvas architecture: persistent burn canvas + cleared-per-frame
  spark overlay to prevent pixel accumulation
- Smooth quadraticCurveTo rendering for fluid signature strokes
- Sparks with motion trails, multi-layer tip glow

Infrastructure:
- Add init() support for command demos — JS can now execute after
  demo HTML is inserted into the DOM
- Fix split-compare retriggerAnimations to not destroy canvas elements
  (clone-and-replace for CSS-only demos, individual retrigger when
  canvas is present)
- Add deep linking to commands (#cmd-overdrive etc.) with hash
  tracking and initial load support
- Remove auto-#hero hash — hero is the default state

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/js/utils/scroll.js

@@ -22,6 +22,21 @@ export function initHashTracking() {
 	let ticking = false;
 
 	function updateHash() {
+		// Don't override command deep links while user is in the commands section
+		if (currentHash.startsWith('cmd-')) {
+			const cmdEl = document.getElementById(currentHash);
+			if (cmdEl) {
+				const rect = cmdEl.getBoundingClientRect();
+				// Only clear the cmd hash if user scrolled well away from commands section
+				if (rect.top > window.innerHeight * 2 || rect.bottom < -window.innerHeight) {
+					currentHash = '';
+				} else {
+					ticking = false;
+					return;
+				}
+			}
+		}
+
 		const scrollY = window.scrollY;
 		const viewportHeight = window.innerHeight;
 		const triggerPoint = scrollY + viewportHeight * 0.3;
@@ -38,6 +53,9 @@ export function initHashTracking() {
 			}
 		});
 
+		// Don't set #hero — it's the default state, no hash needed
+		if (activeSection === 'hero') activeSection = '';
+
 		if (activeSection !== currentHash) {
 			currentHash = activeSection;
 			if (activeSection) {
@@ -59,17 +77,23 @@ export function initHashTracking() {
 
 	// Handle initial hash on page load - instant jump
 	if (window.location.hash) {
-		const target = document.querySelector(window.location.hash);
+		const hash = window.location.hash.slice(1);
+		const target = document.getElementById(hash);
 		if (target) {
+			currentHash = hash;
 			setTimeout(() => {
 				const offset = 40;
 				const targetPosition = target.getBoundingClientRect().top + window.scrollY - offset;
 				window.scrollTo({ top: targetPosition, behavior: 'auto' });
+
+				// If it's a command deep link, activate it
+				if (hash.startsWith('cmd-') && target.classList.contains('manual-entry')) {
+					target.click();
+				}
 			}, 100);
 		}
+	} else {
+		// No hash — don't set one on initial load
 	}
-
-	// Initial check
-	updateHash();
 }