fix: service worker cache busting — unregister old sw on load, bump cache version, stop caching HTML

- Bump sw.js cache from v2 to v3
- Unregister all old service workers on page load
- Stop caching HTML/navigation (caused stale CSS refs after rebuild)

src/components/site-header.tsx

@@ -89,7 +89,7 @@ export async function SiteHeader() {
 							<h1
 								className="font-black tracking-tight leading-none text-white"
 								style={{
-									fontFamily: "var(--font-pixel)",
+									fontFamily: "var(--font-nunito)",
 									fontSize: "clamp(2.8rem, 8vw, 5.5rem)",
 									textShadow:
 										"0 2px 20px rgba(0,0,0,0.4), 0 8px 40px rgba(0,0,0,0.2)",