feat: add Extensible to hero tagline

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: null0NULL123

src/components/HeroSection.astro

@@ -9,7 +9,7 @@
       <span class="line fade-up delay-2">Explore</span>
       <span class="line accent fade-up delay-3">the Frontier</span>
     </h1>
-    <div class="tagline fade-up delay-4">Minimal · Fast · Orderly</div>
+    <div class="tagline fade-up delay-4">Minimal · Fast · Orderly · Extensible</div>
     <div class="cta-group fade-up delay-5">
       <a href="https://blog.iocussl.dpdns.org" class="btn-primary">Read Blog</a>
       <a href="https://github.com/null0NULL123" class="btn-ghost">Learn More</a>